Added gofmt to format command

Fixes #716 #715

.dockerignore

@@ -1 +1 @@
-bin
+bin/*

.github/FUNDING.yml

@@ -0,0 +1 @@
+github: mikefarah

.github/ISSUE_TEMPLATE/bug_report_v3.md

@@ -1,8 +1,8 @@
 ---
-name: Bug report
+name: Bug report - V3
 about: Create a report to help us improve
 title: ''
-labels: bug
+labels: bug, v3
 assignees: ''
 
 ---
@@ -10,11 +10,14 @@ assignees: ''
 **Describe the bug**
 A clear and concise description of what the bug is.
 
-version of yq: 
-operating system:
+Note that any how to questions should be posted in the discussion board and not raised as an issue.
+
+Version of yq: 3.X.X
+Operating system: mac/linux/windows/....
+Installed via: docker/binary release/homebrew/snap/...
 
 **Input Yaml**
-Concise yaml document(s) (as simple as possible to show the bug)
+Concise yaml document(s) (as simple as possible to show the bug, please keep it to 10 lines or less)
 data1.yml:
 ```yaml
 this: should really work

.github/ISSUE_TEMPLATE/bug_report_v4.md

@@ -0,0 +1,51 @@
+---
+name: Bug report - V4
+about: Create a report to help us improve
+title: ''
+labels: bug, v4
+assignees: ''
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+Note that any how to questions should be posted in the discussion board and not raised as an issue.
+
+Version of yq: 4.X.X
+Operating system: mac/linux/windows/....
+Installed via: docker/binary release/homebrew/snap/...
+
+**Input Yaml**
+Concise yaml document(s) (as simple as possible to show the bug, please keep it to 10 lines or less)
+data1.yml:
+```yaml
+this: should really work
+```
+
+data2.yml:
+```yaml
+but: it strangely didn't
+```
+
+**Command**
+The command you ran:
+```
+yq eval-all 'select(fileIndex==0) | .a.b.c' data1.yml data2.yml
+```
+
+**Actual behavior**
+
+```yaml
+cat: meow
+```
+
+**Expected behavior**
+
+```yaml
+this: should really work
+but: it strangely didn't
+```
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/feature_request.md

@@ -1,17 +1,23 @@
 ---
-name: Feature request
+name: Feature request - V4
 about: Suggest an idea for this project
 title: ''
-labels: enhancement
+labels: enhancement, v4
 assignees: ''
 
 ---
 
-**Is your feature request related to a problem? Please describe.**
-A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+**Please describe your feature request.**
+A clear and concise description of what the request is and what it would solve. 
+Eg. I wish I could use yq to [...]
+
+Note:
+- how to questions should be posted in the discussion board and not raised as an issue.
+- V3 will no longer have any enhancements.
 
 **Describe the solution you'd like**
 If we have data1.yml like:
+(please keep to around 10 lines )
 
 ```yaml
 country: Australia
@@ -20,7 +26,7 @@ country: Australia
 And we run a command:
 
 ```bash
-yq predictWeather data1.yml
+yq eval 'predictWeatherOf(.country)'
 ```
 
 it could output

.github/workflows/go.yml

@@ -28,7 +28,4 @@ jobs:
       run: |
         export PATH=${PATH}:`go env GOPATH`/bin
         scripts/devtools.sh
-    - name: Build
-      run: |
-        export PATH=${PATH}:`go env GOPATH`/bin
         make local build

.github/workflows/release.yml

@@ -0,0 +1,70 @@
+name: Release YQ
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  publishGitRelease:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-go@v2
+        with:
+          go-version: '^1.15'
+      - name: Cross compile
+        run: |
+          sudo apt-get install rhash -y
+          go get github.com/mitchellh/gox
+          ./scripts/xcompile.sh
+
+      - name: Create Release
+        id: create_release
+        uses: actions/create-release@v1.0.0
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          tag_name: ${{ github.ref }}
+          release_name: ${{ github.ref }}
+          draft: true
+          prerelease: false
+
+      - uses: shogo82148/actions-upload-release-asset@v1
+        with:
+          upload_url: ${{ steps.create_release.outputs.upload_url }}
+          asset_path: build/*
+
+  publishDocker:
+    environment: dockerhub
+    env:
+      IMAGE_NAME: mikefarah/yq
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+        with:
+          platforms: all
+  
+      - name: Set up Docker Buildx
+        id: buildx
+        uses: docker/setup-buildx-action@v1
+        with:
+          version: latest
+
+      - name: Available platforms
+        run: echo ${{ steps.buildx.outputs.platforms }} && docker version
+ 
+      - name: Build and push image
+        run: |
+          IMAGE_V_VERSION="$(git describe --tags --abbrev=0)"
+          IMAGE_VERSION=${IMAGE_V_VERSION:1}
+
+          SHORT_SHA1=$(git rev-parse --short HEAD)
+          PLATFORMS="linux/amd64,linux/ppc64le,linux/arm64"
+          echo "Building and pushing version ${IMAGE_VERSION} of image ${IMAGE_NAME}"
+          echo ${{ secrets.DOCKER_PASSWORD }} | docker login -u ${{ secrets.DOCKER_USERNAME }} --password-stdin
+          docker buildx build --platform "${PLATFORMS}" -t "${IMAGE_NAME}:${IMAGE_VERSION}"  -t "${IMAGE_NAME}:latest" -t "${IMAGE_NAME}:4" \
+            --push .
+    

Dockerfile

@@ -12,7 +12,7 @@ RUN CGO_ENABLED=0 make local build
 
 # Choose alpine as a base image to make this useful for CI, as many
 # CI tools expect an interactive shell inside the container
-FROM alpine:3.12 as production
+FROM alpine:3.12.3 as production
 
 COPY --from=builder /go/src/mikefarah/yq/yq /usr/bin/yq
 RUN chmod +x /usr/bin/yq

Dockerfile.dev

@@ -4,27 +4,7 @@ COPY scripts/devtools.sh /opt/devtools.sh
 
 RUN set -e -x \
     && /opt/devtools.sh
-
-# install mkdocs
-RUN set -ex \
-    && buildDeps=' \
-        build-essential \
-        python3-dev \
-    ' \
-    && apt-get update && apt-get install -y --no-install-recommends \
-        $buildDeps \
-        python3 \
-        python3-setuptools \
-        python3-wheel \
-        python3-pip \
-    && pip3 install --upgrade \
-        pip \
-        'Markdown>=2.6.9' \
-        'mkdocs>=0.16.3' \
-        'mkdocs-material>=1.10.1' \
-        'markdown-include>=0.5.1' \
-    && apt-get purge -y --auto-remove $buildDeps \
-    && rm -rf /var/lib/apt/lists/*
+ENV PATH=/go/bin:$PATH
 
 ENV CGO_ENABLED 0
 ENV GOPATH /go:/yq

Makefile

@@ -17,6 +17,7 @@ help:
 	@echo '    make vendor          Install dependencies to vendor directory.'
 	@echo '    make format          Run code formatter.'
 	@echo '    make check           Run static code analysis (lint).'
+	@echo '    make secure          Run gosec.'
 	@echo '    make test            Run tests on project.'
 	@echo '    make cover           Run tests and capture code coverage metrics on project.'
 	@echo '    make clean           Clean the directory tree of produced artifacts.'
@@ -84,6 +85,10 @@ format: vendor
 check: format
 	${DOCKRUN} bash ./scripts/check.sh
 
+.PHONY: secure
+secure: 
+	${DOCKRUN} bash ./scripts/secure.sh
+
 .PHONY: test
 test: check
 	${DOCKRUN} bash ./scripts/test.sh
@@ -96,11 +101,6 @@ cover: check
 	@find cover -type d -exec chmod 755 {} \; || :
 	@find cover -type f -exec chmod 644 {} \; || :
 
-.PHONY: build-docs
-build-docs: prepare mkdocs.yml mkdocs/*
-	${DOCKRUN} mkdocs build
-	@find docs -type d -exec chmod 755 {} \; || :
-	@find docs -type f -exec chmod 644 {} \; || :
 
 .PHONY: release
 release: xcompile

README.md

@@ -3,24 +3,64 @@
 ![Build](https://github.com/mikefarah/yq/workflows/Build/badge.svg)  ![Docker Pulls](https://img.shields.io/docker/pulls/mikefarah/yq.svg) ![Github Releases (by Release)](https://img.shields.io/github/downloads/mikefarah/yq/total.svg) ![Go Report](https://goreportcard.com/badge/github.com/mikefarah/yq)
 
 
-a lightweight and portable command-line YAML processor
+a lightweight and portable command-line YAML processor. `yq` uses [jq](https://github.com/stedolan/jq) like syntax but works with yaml files as well as json. It doesn't yet support everything `jq` does - but it does support the most common operations and functions, and more is being added continuously.
 
-The aim of the project is to be the [jq](https://github.com/stedolan/jq) or sed of yaml files.
+yq is written in go - so you can download a dependency free binary for your platform and you are good to go! If you prefer there are a variety of package managers that can be used as well as docker, all listed below.
+
+## V4 released!
+V4 is now officially released, it's quite different from V3 (sorry for the migration), however it is much more similar to ```jq```, using a similar expression syntax and therefore support much more complex functionality! 
+
+If you've been using v3 and want/need to upgrade, checkout the [upgrade guide](https://mikefarah.gitbook.io/yq/v/v4.x/upgrading-from-v3).
+
+Support for v3 will cease August 2021, until then, critical bug and security fixes will still get applied if required.
 
 ## Install
 
 ### [Download the latest binary](https://github.com/mikefarah/yq/releases/latest)
 
-### MacOS:
+### wget
+Use wget to download the pre-compiled binaries:
+
+#### Compressed via tar.gz
+```bash
+wget https://github.com/mikefarah/yq/releases/download/${VERSION}/${BINARY}.tar.gz -O - |\
+  tar xz && mv ${BINARY} /usr/bin/yq
+```
+
+#### Plain binary
+
+```bash
+wget https://github.com/mikefarah/yq/releases/download/${VERSION}/${BINARY} -O /usr/bin/yq &&\
+    chmod +x /usr/bin/yq
+```
+
+For instance, VERSION=v4.2.0 and BINARY=yq_linux_amd64
+
+### MacOS / Linux via Homebrew:
+Using [Homebrew](https://brew.sh/)
 ```
 brew install yq
 ```
 
-### Ubuntu and other Linux distros supporting `snap` packages:
+or, for the (deprecated) v3 version:
+
+```
+brew install yq@3
+```
+
+Note that for v3, as it is a versioned brew it will not add the `yq` command to your path automatically. Please follow the instructions given by brew upon installation.
+
+### Linux via snap:
 ```
 snap install yq
 ```
 
+or, for the (deprecated) v3 version:
+
+```
+snap install yq --channel=v3/stable
+```
+
 #### Snap notes
 `yq` installs with [_strict confinement_](https://docs.snapcraft.io/snap-confinement/6233) in snap, this means it doesn't have direct access to root files. To read root files you can:
 
@@ -39,18 +79,6 @@ sudo mv /etc/myfile.tmp /etc/myfile
 rm /etc/myfile.tmp
 ```
 
-### wget
-
-Use wget to download the pre-compiled binaries:
-
-```bash
-wget https://github.com/mikefarah/yq/releases/download/{VERSION}/{BINARY} -O /usr/bin/yq &&\
-    chmod +x /usr/bin/yq
-```
-
-For instance, VERSION=4.0.0 and BINARY=yq_linux_amd64
-
-
 ### Run with Docker
 
 #### Oneshot use:
@@ -62,7 +90,7 @@ docker run --rm -v "${PWD}":/workdir mikefarah/yq <command> [flags] [expression
 #### Run commands interactively:
 
 ```bash
-docker run --rm -it -v "${PWD}":/workdir mikefarah/yq sh
+docker run --rm -it -v "${PWD}":/workdir --entrypoint sh mikefarah/yq
 ```
 
 It can be useful to have a bash function to avoid typing the whole docker command:
@@ -81,13 +109,31 @@ GO111MODULE=on go get github.com/mikefarah/yq/v4
 ## Community Supported Installation methods
 As these are supported by the community :heart: - however, they may be out of date with the officially supported releases.
 
+# Webi
+
+```
+webi yq
+```
+
+See [webi](https://webinstall.dev/)
+Supported by @adithyasunil26 (https://github.com/webinstall/webi-installers/tree/master/yq)
 
 ### Windows:
+[![Chocolatey](https://img.shields.io/chocolatey/v/yq.svg)](https://chocolatey.org/packages/yq)
+[![Chocolatey](https://img.shields.io/chocolatey/dt/yq.svg)](https://chocolatey.org/packages/yq)
 ```
 choco install yq
 ```
 Supported by @chillum (https://chocolatey.org/packages/yq)
 
+### Mac:
+Using [MacPorts](https://www.macports.org/)
+```
+sudo port selfupdate
+sudo port install yq
+```
+Supported by @herbygillot (https://ports.macports.org/maintainer/github/herbygillot)
+
 ### Alpine Linux
 - Enable edge/community repo by adding ```$MIRROR/alpine/edge/community``` to ```/etc/apk/repositories```
 - Update database index with ```apk update```
@@ -107,22 +153,21 @@ sudo apt install yq -y
 Supported by @rmescandon (https://launchpad.net/~rmescandon/+archive/ubuntu/yq)
 
 ## Features
+- [Detailed documentation with many examples](https://mikefarah.gitbook.io/yq/)
 - Written in portable go, so you can download a lovely dependency free binary
+- Uses similar syntax as `jq` but works with YAML and JSON files
+- Fully supports multi document yaml files
 - Colorized yaml output
-- [Deep read a yaml file with a given path expression](https://mikefarah.gitbook.io/yq/v/v4.x/traverse)
-- [Return the lengths of arrays/object/scalars](https://mikefarah.gitbook.io/yq/commands/read#printing-length-of-the-results)
-- Update a yaml file given a [path expression](https://mikefarah.gitbook.io/yq/commands/write-update#basic) or [script file](https://mikefarah.gitbook.io/yq/commands/write-update#basic)
-- Update creates any missing entries in the path on the fly
-- Deeply [compare](https://mikefarah.gitbook.io/yq/commands/compare) yaml files
-- Keeps yaml formatting and comments when updating
-- [Validate a yaml file](https://mikefarah.gitbook.io/yq/commands/validate)
-- Create a yaml file given a [deep path and value](https://mikefarah.gitbook.io/yq/commands/create#creating-a-simple-yaml-file) or a [script file](https://mikefarah.gitbook.io/yq/commands/create#creating-using-a-create-script)
-- [Prefix a path to a yaml file](https://mikefarah.gitbook.io/yq/commands/prefix)
-- [Convert to/from json to yaml](https://mikefarah.gitbook.io/yq/usage/convert)
-- [Pipe data in by using '-'](https://mikefarah.gitbook.io/yq/commands/read#from-stdin)
-- [Merge](https://mikefarah.gitbook.io/yq/commands/merge) multiple yaml files with various options for [overriding](https://mikefarah.gitbook.io/yq/commands/merge#overwrite-values) and [appending](https://mikefarah.gitbook.io/yq/commands/merge#append-values-with-arrays)
-- Supports multiple documents in a single yaml file for [reading](https://mikefarah.gitbook.io/yq/commands/read#multiple-documents), [writing](https://mikefarah.gitbook.io/yq/commands/write-update#multiple-documents) and [merging](https://mikefarah.gitbook.io/yq/commands/merge#multiple-documents)
-- General shell completion scripts (bash/zsh/fish/powershell) (https://mikefarah.gitbook.io/yq/commands/shell-completion)
+- [Deeply traverse yaml](https://mikefarah.gitbook.io/yq/operators/traverse-read)
+- [Sort yaml by keys](https://mikefarah.gitbook.io/yq/operators/sort-keys)
+- Manipulate yaml [comments](https://mikefarah.gitbook.io/yq/operators/comment-operators), [styling](https://mikefarah.gitbook.io/yq/operators/style), [tags](https://mikefarah.gitbook.io/yq/operators/tag) and [anchors and aliases](https://mikefarah.gitbook.io/yq/operators/anchor-and-alias-operators).
+- [Update yaml inplace](https://mikefarah.gitbook.io/yq/v/v4.x/commands/evaluate#flags)
+- [Complex expressions to select and update](https://mikefarah.gitbook.io/yq/operators/select#select-and-update-matching-values-in-map)
+- Keeps yaml formatting and comments when updating (though there are issues with whitespace)
+- [Convert to/from json to yaml](https://mikefarah.gitbook.io/yq/v/v4.x/usage/convert)
+- [Pipe data in by using '-'](https://mikefarah.gitbook.io/yq/v/v4.x/commands/evaluate)
+- [General shell completion scripts (bash/zsh/fish/powershell)](https://mikefarah.gitbook.io/yq/v/v4.x/commands/shell-completion)
+- [Reduce](https://mikefarah.gitbook.io/yq/operators/reduce) to merge multiple files or sum an array or other fancy things.
 
 ## [Usage](https://mikefarah.gitbook.io/yq/)
 
@@ -134,32 +179,33 @@ Usage:
   yq [command]
 
 Available Commands:
-  compare          yq x [--prettyPrint/-P] dataA.yaml dataB.yaml 'b.e(name==fr*).value'
-  delete           yq d [--inplace/-i] [--doc/-d index] sample.yaml 'b.e(name==fred)'
+  eval             Apply expression to each document in each yaml file given in sequence
+  eval-all         Loads _all_ yaml documents of _all_ yaml files and runs expression once
   help             Help about any command
-  merge            yq m [--inplace/-i] [--doc/-d index] [--overwrite/-x] [--append/-a] sample.yaml sample2.yaml
-  new              yq n [--script/-s script_file] a.b.c newValue
-  prefix           yq p [--inplace/-i] [--doc/-d index] sample.yaml a.b.c
-  read             yq r [--printMode/-p pv] sample.yaml 'b.e(name==fr*).value'
-  shell-completion Generates shell completion scripts
-  validate         yq v sample.yaml
-  write            yq w [--inplace/-i] [--script/-s script_file] [--doc/-d index] sample.yaml 'b.e(name==fr*).value' newValue
+  shell-completion Generate completion script
 
 Flags:
-  -C, --colors        print with colors
+  -C, --colors        force print with colors
+  -e, --exit-status   set exit status if there are no matches or null or false is returned
   -h, --help          help for yq
   -I, --indent int    sets indent level for output (default 2)
-  -P, --prettyPrint   pretty print
-  -j, --tojson        output as json. By default it prints a json document in one line, use the prettyPrint flag to print a formatted doc.
+  -i, --inplace       update the yaml file inplace of first yaml file given.
+  -M, --no-colors     force print with no colors
+  -N, --no-doc        Don't print document separators (---)
+  -n, --null-input    Don't read input, simply evaluate the expression given. Useful for creating yaml docs from scratch.
+  -P, --prettyPrint    pretty print, shorthand for '... style = ""' 
+  -j, --tojson        output as json. Set indent to 0 to print json in one line.
   -v, --verbose       verbose mode
   -V, --version       Print version information and quit
 
 Use "yq [command] --help" for more information about a command.
 ```
 
-## Upgrade from V2
-If you've been using v2 and want/need to upgrade, checkout the [upgrade guide](https://mikefarah.gitbook.io/yq/upgrading-from-v2).
+Simple Example:
+
+```bash
+yq e '.a.b | length' f1.yml f2.yml 
+```
 
 ## Known Issues / Missing Features
 - `yq` attempts to preserve comment positions and whitespace as much as possible, but it does not handle all scenarios (see https://github.com/go-yaml/yaml/tree/v3 for details)
-- You cannot (yet) select multiple paths/keys from the yaml to be printed out (https://github.com/mikefarah/yq/issues/287)

cmd/constant.go

@@ -14,5 +14,6 @@ var noDocSeparators = false
 var nullInput = false
 var verbose = false
 var version = false
+var prettyPrint = false
 
 var completedSuccessfully = false

cmd/evaluate_all_command.go

@@ -17,6 +17,9 @@ func createEvaluateAllCommand() *cobra.Command {
 		Example: `
 # merges f2.yml into f1.yml (inplace)
 yq eval-all --inplace 'select(fileIndex == 0) * select(fileIndex == 1)' f1.yml f2.yml		
+
+# use '-' as a filename to read from STDIN
+cat file2.yml | yq ea '.a.b' file1.yml - file3.yml
 `,
 		Long: "Evaluate All:\nUseful when you need to run an expression across several yaml documents or files. Consumes more memory than eval",
 		RunE: evaluateAll,
@@ -42,14 +45,21 @@ func evaluateAll(cmd *cobra.Command, args []string) error {
 		colorsEnabled = true
 	}
 
-	if writeInplace && len(args) < 2 {
+	firstFileIndex := -1
+	if !nullInput && len(args) == 1 {
+		firstFileIndex = 0
+	} else if len(args) > 1 {
+		firstFileIndex = 1
+	}
+
+	if writeInplace && (firstFileIndex == -1) {
 		return fmt.Errorf("Write inplace flag only applicable when giving an expression and at least one file")
 	}
 
 	if writeInplace {
 		// only use colors if its forced
 		colorsEnabled = forceColor
-		writeInPlaceHandler := yqlib.NewWriteInPlaceHandler(args[1])
+		writeInPlaceHandler := yqlib.NewWriteInPlaceHandler(args[firstFileIndex])
 		out, err = writeInPlaceHandler.CreateTempFile()
 		if err != nil {
 			return err
@@ -59,25 +69,29 @@ func evaluateAll(cmd *cobra.Command, args []string) error {
 		defer func() { writeInPlaceHandler.FinishWriteInPlace(completedSuccessfully) }()
 	}
 
+	if nullInput && len(args) > 1 {
+		return errors.New("Cannot pass files in when using null-input flag")
+	}
+
 	printer := yqlib.NewPrinter(out, outputToJSON, unwrapScalar, colorsEnabled, indent, !noDocSeparators)
 
 	allAtOnceEvaluator := yqlib.NewAllAtOnceEvaluator()
 	switch len(args) {
 	case 0:
 		if pipingStdIn {
-			err = allAtOnceEvaluator.EvaluateFiles("", []string{"-"}, printer)
+			err = allAtOnceEvaluator.EvaluateFiles(processExpression(""), []string{"-"}, printer)
 		} else {
 			cmd.Println(cmd.UsageString())
 			return nil
 		}
 	case 1:
 		if nullInput {
-			err = yqlib.NewStreamEvaluator().EvaluateNew(args[0], printer)
+			err = yqlib.NewStreamEvaluator().EvaluateNew(processExpression(args[0]), printer)
 		} else {
-			err = allAtOnceEvaluator.EvaluateFiles("", []string{args[0]}, printer)
+			err = allAtOnceEvaluator.EvaluateFiles(processExpression(""), []string{args[0]}, printer)
 		}
 	default:
-		err = allAtOnceEvaluator.EvaluateFiles(args[0], args[1:], printer)
+		err = allAtOnceEvaluator.EvaluateFiles(processExpression(args[0]), args[1:], printer)
 	}
 
 	completedSuccessfully = err == nil

cmd/evalute_sequence_command.go

@@ -21,6 +21,9 @@ yq e '.a.b | length' f1.yml f2.yml
 # prints out the file
 yq e sample.yaml 
 
+# use '-' as a filename to read from STDIN
+cat file2.yml | yq e '.a.b' file1.yml - file3.yml
+
 # prints a new yaml document
 yq e -n '.a.b.c = "cat"' 
 
@@ -33,6 +36,16 @@ yq e '.a.b = "cool"' -i file.yaml
 	}
 	return cmdEvalSequence
 }
+
+func processExpression(expression string) string {
+	if prettyPrint && expression == "" {
+		return `... style=""`
+	} else if prettyPrint {
+		return fmt.Sprintf("%v | ... style= \"\"", expression)
+	}
+	return expression
+}
+
 func evaluateSequence(cmd *cobra.Command, args []string) error {
 	cmd.SilenceUsage = true
 	// 0 args, read std in
@@ -52,14 +65,21 @@ func evaluateSequence(cmd *cobra.Command, args []string) error {
 		colorsEnabled = true
 	}
 
-	if writeInplace && len(args) < 2 {
+	firstFileIndex := -1
+	if !nullInput && len(args) == 1 {
+		firstFileIndex = 0
+	} else if len(args) > 1 {
+		firstFileIndex = 1
+	}
+
+	if writeInplace && (firstFileIndex == -1) {
 		return fmt.Errorf("Write inplace flag only applicable when giving an expression and at least one file")
 	}
 
 	if writeInplace {
 		// only use colors if its forced
 		colorsEnabled = forceColor
-		writeInPlaceHandler := yqlib.NewWriteInPlaceHandler(args[1])
+		writeInPlaceHandler := yqlib.NewWriteInPlaceHandler(args[firstFileIndex])
 		out, err = writeInPlaceHandler.CreateTempFile()
 		if err != nil {
 			return err
@@ -73,22 +93,26 @@ func evaluateSequence(cmd *cobra.Command, args []string) error {
 
 	streamEvaluator := yqlib.NewStreamEvaluator()
 
+	if nullInput && len(args) > 1 {
+		return errors.New("Cannot pass files in when using null-input flag")
+	}
+
 	switch len(args) {
 	case 0:
 		if pipingStdIn {
-			err = streamEvaluator.EvaluateFiles("", []string{"-"}, printer)
+			err = streamEvaluator.EvaluateFiles(processExpression(""), []string{"-"}, printer)
 		} else {
 			cmd.Println(cmd.UsageString())
 			return nil
 		}
 	case 1:
 		if nullInput {
-			err = streamEvaluator.EvaluateNew(args[0], printer)
+			err = streamEvaluator.EvaluateNew(processExpression(args[0]), printer)
 		} else {
-			err = streamEvaluator.EvaluateFiles("", []string{args[0]}, printer)
+			err = streamEvaluator.EvaluateFiles(processExpression(""), []string{args[0]}, printer)
 		}
 	default:
-		err = streamEvaluator.EvaluateFiles(args[0], args[1:], printer)
+		err = streamEvaluator.EvaluateFiles(processExpression(args[0]), args[1:], printer)
 	}
 	completedSuccessfully = err == nil
 

cmd/root.go

@@ -47,6 +47,8 @@ func New() *cobra.Command {
 	rootCmd.PersistentFlags().IntVarP(&indent, "indent", "I", 2, "sets indent level for output")
 	rootCmd.Flags().BoolVarP(&version, "version", "V", false, "Print version information and quit")
 	rootCmd.PersistentFlags().BoolVarP(&writeInplace, "inplace", "i", false, "update the yaml file inplace of first yaml file given.")
+	rootCmd.PersistentFlags().BoolVarP(&unwrapScalar, "unwrapScalar", "", true, "unwrap scalar, print the value with no quotes, colors or comments")
+	rootCmd.PersistentFlags().BoolVarP(&prettyPrint, "prettyPrint", "P", false, "pretty print, shorthand for '... style = \"\"'")
 	rootCmd.PersistentFlags().BoolVarP(&exitStatus, "exit-status", "e", false, "set exit status if there are no matches or null or false is returned")
 
 	rootCmd.PersistentFlags().BoolVarP(&forceColor, "colors", "C", false, "force print with colors")

cmd/version.go

@@ -11,7 +11,7 @@ var (
 	GitDescribe string
 
 	// Version is main version number that is being run at the moment.
-	Version = "4.0.0-beta1"
+	Version = "4.9.3"
 
 	// VersionPrerelease is a pre-release marker for the version. If this is "" (empty string)
 	// then it means that it is a final release. Otherwise, this is a pre-release

examples/data1.yaml

@@ -1,4 +1,6 @@
-a: simple # just the best
-b: [1, 2]
-c:
-  test: 1
+a:
+  key1: "value1"
+  key2: 2.6
+  ab:
+    key1: 6
+    key2: "h"

github-action/Dockerfile

@@ -1,4 +1,4 @@
-FROM mikefarah/yq:3
+FROM mikefarah/yq:4.9.3
 
 COPY entrypoint.sh /entrypoint.sh
 

go.mod

@@ -1,18 +1,16 @@
 module github.com/mikefarah/yq/v4
 
 require (
-	github.com/elliotchance/orderedmap v1.3.0
-	github.com/fatih/color v1.9.0
-	github.com/goccy/go-yaml v1.8.1
-	github.com/jinzhu/copier v0.0.0-20190924061706-b57f9002281a
-	github.com/mattn/go-colorable v0.1.7 // indirect
-	github.com/spf13/cobra v1.1.1
+	github.com/elliotchance/orderedmap v1.4.0
+	github.com/fatih/color v1.10.0
+	github.com/goccy/go-yaml v1.8.9
+	github.com/jinzhu/copier v0.2.8
+	github.com/spf13/cobra v1.1.3
 	github.com/timtadh/data-structures v0.5.3 // indirect
 	github.com/timtadh/lexmachine v0.2.2
-	golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f // indirect
-	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect
+	golang.org/x/sys v0.0.0-20210317225723-c4fcb01b228e // indirect
 	gopkg.in/op/go-logging.v1 v1.0.0-20160211212156-b2cb9fa56473
-	gopkg.in/yaml.v3 v3.0.0-20200615113413-eeeca48fe776
+	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b
 )
 
 go 1.15

go.sum

@@ -36,22 +36,24 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
 github.com/dgryski/go-sip13 v0.0.0-20181026042036-e10d5fee7954/go.mod h1:vAd38F8PWV+bWy6jNmig1y/TA+kYO4g3RSRF0IAv0no=
-github.com/elliotchance/orderedmap v1.3.0 h1:k6m77/d0zCXTjsk12nX40TkEBkSICq8T4s6R6bpCqU0=
-github.com/elliotchance/orderedmap v1.3.0/go.mod h1:8hdSl6jmveQw8ScByd3AaNHNk51RhbTazdqtTty+NFw=
+github.com/elliotchance/orderedmap v1.4.0 h1:wZtfeEONCbx6in1CZyE6bELEt/vFayMvsxqI5SgsR+A=
+github.com/elliotchance/orderedmap v1.4.0/go.mod h1:wsDwEaX5jEoyhbs7x93zk2H/qv0zwuhg4inXhDkYqys=
 github.com/fatih/color v1.7.0/go.mod h1:Zm6kSWBoL9eyXnKyktHP6abPY2pDugNf5KwzbycvMj4=
-github.com/fatih/color v1.9.0 h1:8xPHl4/q1VyqGIPif1F+1V3Y3lSmrq01EabUW3CoW5s=
-github.com/fatih/color v1.9.0/go.mod h1:eQcE1qtQxscV5RaZvpXrrb8Drkc3/DdQ+uUYCNjL+zU=
+github.com/fatih/color v1.10.0 h1:s36xzo75JdqLaaWoiEHk767eHiwo0598uUxyfiPkDsg=
+github.com/fatih/color v1.10.0/go.mod h1:ELkj/draVOlAH/xkhN6mQ50Qd0MPOk5AAr3maGEBuJM=
 github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
 github.com/ghodss/yaml v1.0.0/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
 github.com/go-kit/kit v0.8.0/go.mod h1:xBxKIO96dXMWWy0MnWVtmwkA9/13aqxPnvrjFYMA2as=
 github.com/go-logfmt/logfmt v0.3.0/go.mod h1:Qt1PoO58o5twSAckw1HlFXLmHsOX5/0LbT9GBnD5lWE=
 github.com/go-logfmt/logfmt v0.4.0/go.mod h1:3RMwSq7FuexP4Kalkev3ejPJsZTpXXBr9+V4qmtdjCk=
+github.com/go-playground/assert/v2 v2.0.1/go.mod h1:VDjEfimB/XKnb+ZQfWdccd7VUvScMdVu0Titje2rxJ4=
 github.com/go-playground/locales v0.13.0/go.mod h1:taPMhCMXrRLJO55olJkUXHZBHCxTMfnGwq/HNwmWNS8=
 github.com/go-playground/universal-translator v0.17.0/go.mod h1:UkSxE5sNxxRwHyU+Scu5vgOQjsIJAF8j9muTVoKLVtA=
+github.com/go-playground/validator/v10 v10.4.1/go.mod h1:nlOn6nFhuKACm19sB/8EGNn9GlaMV7XkbRSipzJ0Ii4=
 github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=
-github.com/goccy/go-yaml v1.8.1 h1:JuZRFlqLM5cWF6A+waL8AKVuCcqvKOuhJtUQI+L3ez0=
-github.com/goccy/go-yaml v1.8.1/go.mod h1:wS4gNoLalDSJxo/SpngzPQ2BN4uuZVLCmbM4S3vd4+Y=
+github.com/goccy/go-yaml v1.8.9 h1:4AEXg2qx+/w29jXnXpMY6mTckmYu1TMoHteKuMf0HFg=
+github.com/goccy/go-yaml v1.8.9/go.mod h1:U/jl18uSupI5rdI2jmuCswEA2htH9eXfferR3KfscvA=
 github.com/gogo/protobuf v1.1.1/go.mod h1:r8qH/GZQm5c6nD/R0oafs1akxWv10x8SbQlK7atdtwQ=
 github.com/gogo/protobuf v1.2.1/go.mod h1:hp+jE20tsWTFYpLwKvXlhS1hjn+gTNwPg2I6zVXpSg4=
 github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
@@ -99,8 +101,8 @@ github.com/hashicorp/memberlist v0.1.3/go.mod h1:ajVTdAv/9Im8oMAAj5G31PhhMCZJV2p
 github.com/hashicorp/serf v0.8.2/go.mod h1:6hOLApaqBFA1NXqRQAsxw9QxuDEvNxSQRwA/JwenrHc=
 github.com/inconshreveable/mousetrap v1.0.0 h1:Z8tu5sraLXCXIcARxBp/8cbvlwVa7Z1NHg9XEKhtSvM=
 github.com/inconshreveable/mousetrap v1.0.0/go.mod h1:PxqpIevigyE2G7u3NXJIT2ANytuPF1OarO4DADm73n8=
-github.com/jinzhu/copier v0.0.0-20190924061706-b57f9002281a h1:zPPuIq2jAWWPTrGt70eK/BSch+gFAGrNzecsoENgu2o=
-github.com/jinzhu/copier v0.0.0-20190924061706-b57f9002281a/go.mod h1:yL958EeXv8Ylng6IfnvG4oflryUi3vgA3xPs9hmII1s=
+github.com/jinzhu/copier v0.2.8 h1:N8MbL5niMwE3P4dOwurJixz5rMkKfujmMRFmAanSzWE=
+github.com/jinzhu/copier v0.2.8/go.mod h1:24xnZezI2Yqac9J61UC6/dG/k76ttpq0DdJI3QmUvro=
 github.com/jonboulle/clockwork v0.1.0/go.mod h1:Ii8DK3G1RaLaWxj9trq07+26W01tbo22gdxWY5EU2bo=
 github.com/json-iterator/go v1.1.6/go.mod h1:+SdeFBvtyEkXs7REEP0seUULqWtbJapLOCVDaaPEHmU=
 github.com/jstemmer/go-junit-report v0.0.0-20190106144839-af01ea7f8024/go.mod h1:6v2b51hI/fHJwM22ozAgKL4VKDeJcHhJFhtBdhmNjmU=
@@ -118,15 +120,9 @@ github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/leodido/go-urn v1.2.0/go.mod h1:+8+nEpDfqqsY+g338gtMEUOtuK+4dEMhiQEgxpxOKII=
 github.com/magiconair/properties v1.8.1/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czPbwD3XqdrwzmxQ=
 github.com/mattn/go-colorable v0.0.9/go.mod h1:9vuHe8Xs5qXnSaW/c/ABM9alt+Vo+STaOChaDxuIBZU=
-github.com/mattn/go-colorable v0.1.4 h1:snbPLB8fVfU9iwbbo30TPtbLRzwWu6aJS6Xh4eaaviA=
-github.com/mattn/go-colorable v0.1.4/go.mod h1:U0ppj6V5qS13XJ6of8GYAs25YV2eR4EVcfRqFIhoBtE=
-github.com/mattn/go-colorable v0.1.7 h1:bQGKb3vps/j0E9GfJQ03JyhRuxsvdAanXlT9BTw3mdw=
-github.com/mattn/go-colorable v0.1.7/go.mod h1:u6P/XSegPjTcexA+o6vUJrdnUu04hMope9wVRipJSqc=
+github.com/mattn/go-colorable v0.1.8 h1:c1ghPdyEDarC70ftn0y+A/Ee++9zz8ljHG1b13eJ0s8=
+github.com/mattn/go-colorable v0.1.8/go.mod h1:u6P/XSegPjTcexA+o6vUJrdnUu04hMope9wVRipJSqc=
 github.com/mattn/go-isatty v0.0.3/go.mod h1:M+lRXTBqGeGNdLjl/ufCoiOlB5xdOkqRJdNxMWT7Zi4=
-github.com/mattn/go-isatty v0.0.8/go.mod h1:Iq45c/XA43vh69/j3iqttzPXn0bhXyGjM0Hdxcsrc5s=
-github.com/mattn/go-isatty v0.0.10/go.mod h1:qgIWMr58cqv1PHHyhnkY9lrL7etaEgOFcMEpPG5Rm84=
-github.com/mattn/go-isatty v0.0.11 h1:FxPOTFNqGkuDUGi3H/qkUbQO4ZiBa2brKq5r0l8TGeM=
-github.com/mattn/go-isatty v0.0.11/go.mod h1:PhnuNfih5lzO57/f3n+odYbM4JtupLOxQOAqxQCu2WE=
 github.com/mattn/go-isatty v0.0.12 h1:wuysRhFDzyxgEmMf5xjvJ2M9dZoWAXNNr5LSBS7uHXY=
 github.com/mattn/go-isatty v0.0.12/go.mod h1:cbi8OIDigv2wuxKPP5vlRcQ1OAZbq2CE4Kysco4FUpU=
 github.com/matttproud/golang_protobuf_extensions v1.0.1/go.mod h1:D8He9yQNgCq6Z5Ld7szi9bcBfOoFv/3dc6xSMkL2PC0=
@@ -172,10 +168,9 @@ github.com/soheilhy/cmux v0.1.4/go.mod h1:IM3LyeVVIOuxMH7sFAkER9+bJ4dT7Ms6E4xg4k
 github.com/spaolacci/murmur3 v0.0.0-20180118202830-f09979ecbc72/go.mod h1:JwIasOWyU6f++ZhiEuf87xNszmSA2myDM2Kzu9HwQUA=
 github.com/spf13/afero v1.1.2/go.mod h1:j4pytiNVoe2o6bmDsKpLACNPDBIoEAkihy7loJ1B0CQ=
 github.com/spf13/cast v1.3.0/go.mod h1:Qx5cxh0v+4UWYiBimWS+eyWzqEqokIECu5etghLkUJE=
-github.com/spf13/cobra v1.1.1 h1:KfztREH0tPxJJ+geloSLaAkaPkr4ki2Er5quFV1TDo4=
-github.com/spf13/cobra v1.1.1/go.mod h1:WnodtKOvamDL/PwE2M4iKs8aMDBZ5Q5klgD3qfVJQMI=
+github.com/spf13/cobra v1.1.3 h1:xghbfqPkxzxP3C/f3n5DdpAbdKLj4ZE4BWQI362l53M=
+github.com/spf13/cobra v1.1.3/go.mod h1:pGADOWyqRD/YMrPZigI/zbliZ2wVD/23d+is3pSWzOo=
 github.com/spf13/jwalterweatherman v1.0.0/go.mod h1:cQK4TGJAtQXfYWX+Ddv3mKDzgVb68N+wFjFa4jdeBTo=
-github.com/spf13/pflag v1.0.3 h1:zPAT6CGy6wXeQ7NtTnaTerfKOsV6V6F8agHXFiazDkg=
 github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
 github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
 github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
@@ -184,8 +179,9 @@ github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+
 github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
-github.com/stretchr/testify v1.4.0 h1:2E4SXV/wtOkTonXsotYi4li6zVWxYlZuYNCXe9XRJyk=
 github.com/stretchr/testify v1.4.0/go.mod h1:j7eGeouHqKxXV5pUuKE4zz7dFj8WfuZ+81PSLYec5m4=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/subosito/gotenv v1.2.0/go.mod h1:N0PQaV/YGNqwC0u51sEeR/aUtSLEXKX9iv69rRypqCw=
 github.com/timtadh/data-structures v0.5.3 h1:F2tEjoG9qWIyUjbvXVgJqEOGJPMIiYn7U5W5mE+i/vQ=
 github.com/timtadh/data-structures v0.5.3/go.mod h1:9R4XODhJ8JdWFEI8P/HJKqxuJctfBQw6fDibMQny2oU=
@@ -204,6 +200,7 @@ golang.org/x/crypto v0.0.0-20181029021203-45a5f77698d3/go.mod h1:6SG95UA2DQfeDnf
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20190510104115-cbcb75029529/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
 golang.org/x/crypto v0.0.0-20190605123033-f99c8df09eb5/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20190510132918-efd6b22b2522/go.mod h1:ZjyILWgesfNpC6sMxTJOJm9Kp84zZh5NQWvqDGG3Qr8=
@@ -251,21 +248,16 @@ golang.org/x/sys v0.0.0-20181026203630-95b1ffbd15a5/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20181107165924-66b7b1311ac8/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181116152217-5ac8a444bdc5/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
-golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190312061237-fead79001313/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190502145724-3ef323f4f1fd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190507160741-ecd444e8653b/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190606165138-5da285871e9c/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190624142023-c5567b49c5d0/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20191008105621-543471e840be/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20191010194322-b09406accb47/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20191026070338-33540a1f6037 h1:YyJpGZS1sBuBCzLAR1VEpK193GlqGZbnPFnPV/5Rsb4=
-golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200116001909-b77594299b42/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20200223170610-d5e6a3e2c0ae/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f h1:+Nyd8tzPX9R7BWHguqsrbFdRx3WQ/1ib8I44HXV5yTA=
-golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210317225723-c4fcb01b228e h1:XNp2Flc/1eWQGk5BLzqTAN7fQIwIbfyVTuVxXxZh73M=
+golang.org/x/sys v0.0.0-20210317225723-c4fcb01b228e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.1-0.20180807135948-17ff2d5776d2/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.2/go.mod h1:bEr9sfX3Q8Zfm5fL9x+3itogRgK3+ptLWKqgva+5dAk=
@@ -275,7 +267,6 @@ golang.org/x/tools v0.0.0-20180221164845-07fd8470d635/go.mod h1:n7NCudcB/nEzxVGm
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190114222345-bf090417da8b/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190226205152-f727befe758c/go.mod h1:9Yl7xja0Znq3iFh3HoIrodX9oNMXvdceNzlUR8zjMvY=
-golang.org/x/tools v0.0.0-20190311212946-11955173bddd h1:/e+gpKk9r3dJobndpTytxS2gOy6m5uvpg+ISQoEcusQ=
 golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190312151545-0bb0c0a6e846/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20190312170243-e65039ee4138/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
@@ -290,8 +281,6 @@ golang.org/x/tools v0.0.0-20190911174233-4f2ddba30aff/go.mod h1:b+2E5dAYhXwXZwtn
 golang.org/x/tools v0.0.0-20191012152004-8de300cfc20a/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/tools v0.0.0-20191112195655-aa38f8e97acc/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
-golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898 h1:/atklqdjdhuosWIl6AIbOeHJjicWYPqR9bpxqxYG2pA=
-golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 h1:go1bK/D/BFZV2I8cIQd1NKEZ+0owSTG1fDTci4IqFcE=
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 google.golang.org/api v0.4.0/go.mod h1:8k5glujaEP+g9n7WNsDg8QP6cUVNI86fCNMcbazEtwE=
@@ -316,26 +305,22 @@ google.golang.org/grpc v1.19.0/go.mod h1:mqu4LbDTu4XGKhr4mRzUsmM4RtVoemTSY81AxZi
 google.golang.org/grpc v1.20.1/go.mod h1:10oTOabMzJvdu6/UiuZezV6QK5dSlG84ov/aaiqXj38=
 google.golang.org/grpc v1.21.1/go.mod h1:oYelfM1adQP15Ek0mdvEgi9Df8B9CZIaU1084ijfRaM=
 gopkg.in/alecthomas/kingpin.v2 v2.2.6/go.mod h1:FMv+mEhP44yOT+4EoQTLFTRgOQ1FBLkstjWtayDeSgw=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=
-gopkg.in/go-playground/assert.v1 v1.2.1/go.mod h1:9RXL0bg/zibRAgZUYszZSwO/z8Y/a8bDuhia5mkpMnE=
-gopkg.in/go-playground/validator.v9 v9.30.0/go.mod h1:+c9/zcJMFNgbLvly1L1V+PpxWdVbfP1avr/N00E2vyQ=
 gopkg.in/ini.v1 v1.51.0/go.mod h1:pNLf8WUiyNEtQjuu5G5vTm06TEv9tsIgeAvK8hOrP4k=
 gopkg.in/op/go-logging.v1 v1.0.0-20160211212156-b2cb9fa56473 h1:6D+BvnJ/j6e222UW8s2qTSe3wGBtvo0MbVQG/c5k8RE=
 gopkg.in/op/go-logging.v1 v1.0.0-20160211212156-b2cb9fa56473/go.mod h1:N1eN2tsCx0Ydtgjl4cqmbRCsY4/+z4cYDeqwZTk6zog=
 gopkg.in/resty.v1 v1.12.0/go.mod h1:mDo4pnntr5jdWRML875a/NmxYqAlA73dVijT2AXvQQo=
 gopkg.in/yaml.v2 v2.0.0-20170812160011-eb3733d160e7/go.mod h1:JAlM8MvJe8wmxCU4Bli9HhUf9+ttbYbLASfIpnQbh74=
 gopkg.in/yaml.v2 v2.2.1/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
-gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.2.4/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
-gopkg.in/yaml.v2 v2.2.8 h1:obN1ZagJSUGI0Ek/LBmuj4SNLPfIny3KsKFopxRdj10=
-gopkg.in/yaml.v2 v2.2.8/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
-gopkg.in/yaml.v3 v3.0.0-20200615113413-eeeca48fe776 h1:tQIYjPdBoyREyB9XMu+nnTclpTYkz2zFM+lzLJFO4gQ=
-gopkg.in/yaml.v3 v3.0.0-20200615113413-eeeca48fe776/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v2 v2.4.0/go.mod h1:RDklbk79AGWmwhnvt/jBztapEOGDOx6ZbXqjP6csGnQ=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b h1:h8qDotaEPuJATrMmW04NCwg7v22aHH28wwpauUhK9Oo=
+gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
 honnef.co/go/tools v0.0.0-20190102054323-c2f93a96b099/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
 honnef.co/go/tools v0.0.0-20190106161140-3f1c8253044a/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
 honnef.co/go/tools v0.0.0-20190418001031-e561f6794a2a/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=

pkg/yqlib/all_at_once_evaluator.go

@@ -1,29 +1,54 @@
 package yqlib
 
-import "container/list"
+import (
+	"container/list"
 
-/**
-	Loads all yaml documents of all files given into memory, then runs the given expression once.
-**/
+	yaml "gopkg.in/yaml.v3"
+)
+
+// A yaml expression evaluator that runs the expression once against all files/nodes in memory.
 type Evaluator interface {
 	EvaluateFiles(expression string, filenames []string, printer Printer) error
+
+	// EvaluateNodes takes an expression and one or more yaml nodes, returning a list of matching candidate nodes
+	EvaluateNodes(expression string, nodes ...*yaml.Node) (*list.List, error)
+
+	// EvaluateCandidateNodes takes an expression and list of candidate nodes, returning a list of matching candidate nodes
+	EvaluateCandidateNodes(expression string, inputCandidateNodes *list.List) (*list.List, error)
 }
 
 type allAtOnceEvaluator struct {
 	treeNavigator DataTreeNavigator
-	treeCreator   PathTreeCreator
+	treeCreator   ExpressionParser
 }
 
 func NewAllAtOnceEvaluator() Evaluator {
-	return &allAtOnceEvaluator{treeNavigator: NewDataTreeNavigator(), treeCreator: NewPathTreeCreator()}
+	return &allAtOnceEvaluator{treeNavigator: NewDataTreeNavigator(), treeCreator: NewExpressionParser()}
+}
+
+func (e *allAtOnceEvaluator) EvaluateNodes(expression string, nodes ...*yaml.Node) (*list.List, error) {
+	inputCandidates := list.New()
+	for _, node := range nodes {
+		inputCandidates.PushBack(&CandidateNode{Node: node})
+	}
+	return e.EvaluateCandidateNodes(expression, inputCandidates)
+}
+
+func (e *allAtOnceEvaluator) EvaluateCandidateNodes(expression string, inputCandidates *list.List) (*list.List, error) {
+	node, err := e.treeCreator.ParseExpression(expression)
+	if err != nil {
+		return nil, err
+	}
+	context, err := e.treeNavigator.GetMatchingNodes(Context{MatchingNodes: inputCandidates}, node)
+	if err != nil {
+		return nil, err
+	}
+	return context.MatchingNodes, nil
 }
 
 func (e *allAtOnceEvaluator) EvaluateFiles(expression string, filenames []string, printer Printer) error {
 	fileIndex := 0
-	node, err := treeCreator.ParsePath(expression)
-	if err != nil {
-		return err
-	}
+
 	var allDocuments *list.List = list.New()
 	for _, filename := range filenames {
 		reader, err := readStream(filename)
@@ -37,7 +62,7 @@ func (e *allAtOnceEvaluator) EvaluateFiles(expression string, filenames []string
 		allDocuments.PushBackList(fileDocuments)
 		fileIndex = fileIndex + 1
 	}
-	matches, err := treeNavigator.GetMatchingNodes(allDocuments, node)
+	matches, err := e.EvaluateCandidateNodes(expression, allDocuments)
 	if err != nil {
 		return err
 	}

pkg/yqlib/all_at_once_evaluator_test.go

@@ -0,0 +1,40 @@
+package yqlib
+
+import (
+	"testing"
+
+	"github.com/mikefarah/yq/v4/test"
+)
+
+var evaluateNodesScenario = []expressionScenario{
+	{
+		document:   `a: hello`,
+		expression: `.a`,
+		expected: []string{
+			"D0, P[a], (!!str)::hello\n",
+		},
+	},
+	{
+		document:   `a: hello`,
+		expression: `.`,
+		expected: []string{
+			"D0, P[], (doc)::a: hello\n",
+		},
+	},
+	{
+		document:   `- a: "yes"`,
+		expression: `.[] | has("a")`,
+		expected: []string{
+			"D0, P[0], (!!bool)::true\n",
+		},
+	},
+}
+
+func TestAllAtOnceEvaluateNodes(t *testing.T) {
+	var evaluator = NewAllAtOnceEvaluator()
+	for _, tt := range evaluateNodesScenario {
+		node := test.ParseData(tt.document)
+		list, _ := evaluator.EvaluateNodes(tt.expression, &node)
+		test.AssertResultComplex(t, tt.expected, resultsToString(list))
+	}
+}

pkg/yqlib/candidate_node.go

@@ -2,23 +2,55 @@ package yqlib
 
 import (
 	"fmt"
-	"strconv"
-	"strings"
 
 	"github.com/jinzhu/copier"
 	yaml "gopkg.in/yaml.v3"
 )
 
 type CandidateNode struct {
-	Node      *yaml.Node    // the actual node
-	Path      []interface{} /// the path we took to get to this node
-	Document  uint          // the document index of this node
+	Node      *yaml.Node     // the actual node
+	Parent    *CandidateNode // parent node
+	Path      []interface{}  /// the path we took to get to this node
+	Document  uint           // the document index of this node
 	Filename  string
 	FileIndex int
+	// when performing op against all nodes given, this will treat all the nodes as one
+	// (e.g. top level cross document merge). This property does not propegate to child nodes.
+	EvaluateTogether bool
+	IsMapKey         bool
 }
 
 func (n *CandidateNode) GetKey() string {
-	return fmt.Sprintf("%v - %v", n.Document, n.Path)
+	keyPrefix := ""
+	if n.IsMapKey {
+		keyPrefix = "key-"
+	}
+	return fmt.Sprintf("%v%v - %v", keyPrefix, n.Document, n.Path)
+}
+
+func (n *CandidateNode) CreateChild(path interface{}, node *yaml.Node) *CandidateNode {
+	return &CandidateNode{
+		Node:      node,
+		Path:      n.createChildPath(path),
+		Parent:    n,
+		Document:  n.Document,
+		Filename:  n.Filename,
+		FileIndex: n.FileIndex,
+	}
+}
+
+func (n *CandidateNode) createChildPath(path interface{}) []interface{} {
+	if path == nil {
+		newPath := make([]interface{}, len(n.Path))
+		copy(newPath, n.Path)
+		return newPath
+	}
+
+	//don't use append as they may actually modify the path of the orignal node!
+	newPath := make([]interface{}, len(n.Path)+1)
+	copy(newPath, n.Path)
+	newPath[len(n.Path)] = path
+	return newPath
 }
 
 func (n *CandidateNode) Copy() (*CandidateNode, error) {
@@ -32,13 +64,14 @@ func (n *CandidateNode) Copy() (*CandidateNode, error) {
 
 // updates this candidate from the given candidate node
 func (n *CandidateNode) UpdateFrom(other *CandidateNode) {
+
 	n.UpdateAttributesFrom(other)
 	n.Node.Content = other.Node.Content
 	n.Node.Value = other.Node.Value
-	n.Node.Alias = other.Node.Alias
 }
 
 func (n *CandidateNode) UpdateAttributesFrom(other *CandidateNode) {
+	log.Debug("UpdateAttributesFrom: n: %v other: %v", n.GetKey(), other.GetKey())
 	if n.Node.Kind != other.Node.Kind {
 		// clear out the contents when switching to a different type
 		// e.g. map to array
@@ -47,56 +80,22 @@ func (n *CandidateNode) UpdateAttributesFrom(other *CandidateNode) {
 	}
 	n.Node.Kind = other.Node.Kind
 	n.Node.Tag = other.Node.Tag
+	n.Node.Alias = other.Node.Alias
+	n.Node.Anchor = other.Node.Anchor
 
 	// merge will pickup the style of the new thing
 	// when autocreating nodes
 	if n.Node.Style == 0 {
 		n.Node.Style = other.Node.Style
 	}
-	n.Node.FootComment = n.Node.FootComment + other.Node.FootComment
-	n.Node.HeadComment = n.Node.HeadComment + other.Node.HeadComment
-	n.Node.LineComment = n.Node.LineComment + other.Node.LineComment
-}
 
-func (n *CandidateNode) PathStackToString() string {
-	return mergePathStackToString(n.Path)
-}
-
-func mergePathStackToString(pathStack []interface{}) string {
-	var sb strings.Builder
-	for index, path := range pathStack {
-		switch path.(type) {
-		case int, int64:
-			// if arrayMergeStrategy == AppendArrayMergeStrategy {
-			// sb.WriteString("[+]")
-			// } else {
-			sb.WriteString(fmt.Sprintf("[%v]", path))
-			// }
-
-		default:
-			s := fmt.Sprintf("%v", path)
-			var _, errParsingInt = strconv.ParseInt(s, 10, 64) // nolint
-
-			hasSpecial := strings.Contains(s, ".") || strings.Contains(s, "[") || strings.Contains(s, "]") || strings.Contains(s, "\"")
-			hasDoubleQuotes := strings.Contains(s, "\"")
-			wrappingCharacterStart := "\""
-			wrappingCharacterEnd := "\""
-			if hasDoubleQuotes {
-				wrappingCharacterStart = "("
-				wrappingCharacterEnd = ")"
-			}
-			if hasSpecial || errParsingInt == nil {
-				sb.WriteString(wrappingCharacterStart)
-			}
-			sb.WriteString(s)
-			if hasSpecial || errParsingInt == nil {
-				sb.WriteString(wrappingCharacterEnd)
-			}
-		}
-
-		if index < len(pathStack)-1 {
-			sb.WriteString(".")
-		}
+	if other.Node.FootComment != "" {
+		n.Node.FootComment = other.Node.FootComment
+	}
+	if other.Node.HeadComment != "" {
+		n.Node.HeadComment = other.Node.HeadComment
+	}
+	if other.Node.LineComment != "" {
+		n.Node.LineComment = other.Node.LineComment
 	}
-	return sb.String()
 }

pkg/yqlib/color_print.go

@@ -17,8 +17,8 @@ func format(attr color.Attribute) string {
 	return fmt.Sprintf("%s[%dm", escape, attr)
 }
 
-func ColorizeAndPrint(bytes []byte, writer io.Writer) error {
-	tokens := lexer.Tokenize(string(bytes))
+func colorizeAndPrint(yamlBytes []byte, writer io.Writer) error {
+	tokens := lexer.Tokenize(string(yamlBytes))
 	var p printer.Printer
 	p.Bool = func() *printer.Property {
 		return &printer.Property{

pkg/yqlib/context.go

@@ -0,0 +1,68 @@
+package yqlib
+
+import (
+	"container/list"
+
+	"github.com/jinzhu/copier"
+)
+
+type Context struct {
+	MatchingNodes  *list.List
+	Variables      map[string]*list.List
+	DontAutoCreate bool
+}
+
+func (n *Context) SingleReadonlyChildContext(candidate *CandidateNode) Context {
+	list := list.New()
+	list.PushBack(candidate)
+	newContext := n.ChildContext(list)
+	newContext.DontAutoCreate = true
+	return newContext
+}
+
+func (n *Context) SingleChildContext(candidate *CandidateNode) Context {
+	list := list.New()
+	list.PushBack(candidate)
+	return n.ChildContext(list)
+}
+
+func (n *Context) GetVariable(name string) *list.List {
+	if n.Variables == nil {
+		return nil
+	}
+	return n.Variables[name]
+}
+
+func (n *Context) SetVariable(name string, value *list.List) {
+	if n.Variables == nil {
+		n.Variables = make(map[string]*list.List)
+	}
+	n.Variables[name] = value
+}
+
+func (n *Context) ChildContext(results *list.List) Context {
+	clone := Context{}
+	err := copier.Copy(&clone, n)
+	if err != nil {
+		log.Error("Error cloning context :(")
+		panic(err)
+	}
+	clone.MatchingNodes = results
+	return clone
+}
+
+func (n *Context) Clone() Context {
+	clone := Context{}
+	err := copier.Copy(&clone, n)
+	if err != nil {
+		log.Error("Error cloning context :(")
+		panic(err)
+	}
+	return clone
+}
+
+func (n *Context) ReadOnlyClone() Context {
+	clone := n.Clone()
+	clone.DontAutoCreate = true
+	return clone
+}

pkg/yqlib/data_tree_navigator.go

@@ -3,16 +3,14 @@ package yqlib
 import (
 	"fmt"
 
-	"container/list"
-
 	logging "gopkg.in/op/go-logging.v1"
 )
 
 type DataTreeNavigator interface {
-	// given a list of CandidateEntities and a pathNode,
-	// this will process the list against the given pathNode and return
-	// a new list of matching candidates
-	GetMatchingNodes(matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error)
+	// given the context and a expressionNode,
+	// this will process the against the given expressionNode and return
+	// a new context of matching candidates
+	GetMatchingNodes(context Context, expressionNode *ExpressionNode) (Context, error)
 }
 
 type dataTreeNavigator struct {
@@ -22,22 +20,22 @@ func NewDataTreeNavigator() DataTreeNavigator {
 	return &dataTreeNavigator{}
 }
 
-func (d *dataTreeNavigator) GetMatchingNodes(matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	if pathNode == nil {
+func (d *dataTreeNavigator) GetMatchingNodes(context Context, expressionNode *ExpressionNode) (Context, error) {
+	if expressionNode == nil {
 		log.Debugf("getMatchingNodes - nothing to do")
-		return matchingNodes, nil
+		return context, nil
 	}
-	log.Debugf("Processing Op: %v", pathNode.Operation.toString())
+	log.Debugf("Processing Op: %v", expressionNode.Operation.toString())
 	if log.IsEnabledFor(logging.DEBUG) {
-		for el := matchingNodes.Front(); el != nil; el = el.Next() {
+		for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 			log.Debug(NodeToString(el.Value.(*CandidateNode)))
 		}
 	}
 	log.Debug(">>")
-	handler := pathNode.Operation.OperationType.Handler
+	handler := expressionNode.Operation.OperationType.Handler
 	if handler != nil {
-		return handler(d, matchingNodes, pathNode)
+		return handler(d, context, expressionNode)
 	}
-	return nil, fmt.Errorf("Unknown operator %v", pathNode.Operation.OperationType)
+	return Context{}, fmt.Errorf("Unknown operator %v", expressionNode.Operation.OperationType)
 
 }

pkg/yqlib/doc/Add.md

@@ -1,9 +1,9 @@
 Add behaves differently according to the type of the LHS:
 - arrays: concatenate
-- number scalars: arithmetic addition (soon)
-- string scalars: concatenate (soon)
+- number scalars: arithmetic addition
+- string scalars: concatenate
 
-Use `+=` as append assign for things like increment. `.a += .x` is equivalent to running `.a |= . + .x`.
+Use `+=` as append assign for things like increment. Note that `.a += .x` is equivalent to running `.a = .a + .x`.
 
 ## Concatenate and assign arrays
 Given a sample.yml file of:
@@ -67,23 +67,19 @@ will output
 - 2
 ```
 
-## Add object to array
+## Add new object to array
 Given a sample.yml file of:
 ```yaml
 a:
-  - 1
-  - 2
-c:
-  cat: meow
+  - dog: woof
 ```
 then
 ```bash
-yq eval '.a + .c' sample.yml
+yq eval '.a + {"cat": "meow"}' sample.yml
 ```
 will output
 ```yaml
-- 1
-- 2
+- dog: woof
 - cat: meow
 ```
 
@@ -105,7 +101,7 @@ will output
 - hello
 ```
 
-## Update array (append)
+## Append to array
 Given a sample.yml file of:
 ```yaml
 a:
@@ -131,3 +127,113 @@ b:
   - 4
 ```
 
+## Relative append
+Given a sample.yml file of:
+```yaml
+a:
+  a1:
+    b:
+      - cat
+  a2:
+    b:
+      - dog
+  a3: {}
+```
+then
+```bash
+yq eval '.a[].b += ["mouse"]' sample.yml
+```
+will output
+```yaml
+a:
+  a1:
+    b:
+      - cat
+      - mouse
+  a2:
+    b:
+      - dog
+      - mouse
+  a3: {b: [mouse]}
+```
+
+## String concatenation
+Given a sample.yml file of:
+```yaml
+a: cat
+b: meow
+```
+then
+```bash
+yq eval '.a = .a + .b' sample.yml
+```
+will output
+```yaml
+a: catmeow
+b: meow
+```
+
+## Number addition - float
+If the lhs or rhs are floats then the expression will be calculated with floats.
+
+Given a sample.yml file of:
+```yaml
+a: 3
+b: 4.9
+```
+then
+```bash
+yq eval '.a = .a + .b' sample.yml
+```
+will output
+```yaml
+a: 7.9
+b: 4.9
+```
+
+## Number addition - int
+If both the lhs and rhs are ints then the expression will be calculated with ints.
+
+Given a sample.yml file of:
+```yaml
+a: 3
+b: 4
+```
+then
+```bash
+yq eval '.a = .a + .b' sample.yml
+```
+will output
+```yaml
+a: 7
+b: 4
+```
+
+## Increment numbers
+Given a sample.yml file of:
+```yaml
+a: 3
+b: 5
+```
+then
+```bash
+yq eval '.[] += 1' sample.yml
+```
+will output
+```yaml
+a: 4
+b: 6
+```
+
+## Add to null
+Adding to null simply returns the rhs
+
+Running
+```bash
+yq eval --null-input 'null + "cat"'
+```
+will output
+```yaml
+cat
+```
+

pkg/yqlib/doc/Alternative (Default value).md

@@ -0,0 +1,73 @@
+This operator is used to provide alternative (or default) values when a particular expression is either null or false.
+
+## LHS is defined
+Given a sample.yml file of:
+```yaml
+a: bridge
+```
+then
+```bash
+yq eval '.a // "hello"' sample.yml
+```
+will output
+```yaml
+bridge
+```
+
+## LHS is not defined
+Given a sample.yml file of:
+```yaml
+{}
+```
+then
+```bash
+yq eval '.a // "hello"' sample.yml
+```
+will output
+```yaml
+hello
+```
+
+## LHS is null
+Given a sample.yml file of:
+```yaml
+a: ~
+```
+then
+```bash
+yq eval '.a // "hello"' sample.yml
+```
+will output
+```yaml
+hello
+```
+
+## LHS is false
+Given a sample.yml file of:
+```yaml
+a: false
+```
+then
+```bash
+yq eval '.a // "hello"' sample.yml
+```
+will output
+```yaml
+hello
+```
+
+## RHS is an expression
+Given a sample.yml file of:
+```yaml
+a: false
+b: cat
+```
+then
+```bash
+yq eval '.a // .b' sample.yml
+```
+will output
+```yaml
+cat
+```
+

pkg/yqlib/doc/Anchor and Alias Operators.md

@@ -0,0 +1,301 @@
+Use the `alias` and `anchor` operators to read and write yaml aliases and anchors. The `explode` operator normalises a yaml file (dereference (or expands) aliases and remove anchor names).
+
+`yq` supports merge aliases (like `<<: *blah`) however this is no longer in the standard yaml spec (1.2) and so `yq` will automatically add the `!!merge` tag to these nodes as it is effectively a custom tag.
+
+
+## Merge one map
+see https://yaml.org/type/merge.html
+
+Given a sample.yml file of:
+```yaml
+- &CENTER
+  x: 1
+  y: 2
+- &LEFT
+  x: 0
+  y: 2
+- &BIG
+  r: 10
+- &SMALL
+  r: 1
+- !!merge <<: *CENTER
+  r: 10
+```
+then
+```bash
+yq eval '.[4] | explode(.)' sample.yml
+```
+will output
+```yaml
+x: 1
+y: 2
+r: 10
+```
+
+## Merge multiple maps
+see https://yaml.org/type/merge.html
+
+Given a sample.yml file of:
+```yaml
+- &CENTER
+  x: 1
+  y: 2
+- &LEFT
+  x: 0
+  y: 2
+- &BIG
+  r: 10
+- &SMALL
+  r: 1
+- !!merge <<:
+    - *CENTER
+    - *BIG
+```
+then
+```bash
+yq eval '.[4] | explode(.)' sample.yml
+```
+will output
+```yaml
+r: 10
+x: 1
+y: 2
+```
+
+## Override
+see https://yaml.org/type/merge.html
+
+Given a sample.yml file of:
+```yaml
+- &CENTER
+  x: 1
+  y: 2
+- &LEFT
+  x: 0
+  y: 2
+- &BIG
+  r: 10
+- &SMALL
+  r: 1
+- !!merge <<:
+    - *BIG
+    - *LEFT
+    - *SMALL
+  x: 1
+```
+then
+```bash
+yq eval '.[4] | explode(.)' sample.yml
+```
+will output
+```yaml
+r: 10
+x: 1
+y: 2
+```
+
+## Get anchor
+Given a sample.yml file of:
+```yaml
+a: &billyBob cat
+```
+then
+```bash
+yq eval '.a | anchor' sample.yml
+```
+will output
+```yaml
+billyBob
+```
+
+## Set anchor
+Given a sample.yml file of:
+```yaml
+a: cat
+```
+then
+```bash
+yq eval '.a anchor = "foobar"' sample.yml
+```
+will output
+```yaml
+a: &foobar cat
+```
+
+## Set anchor relatively using assign-update
+Given a sample.yml file of:
+```yaml
+a:
+  b: cat
+```
+then
+```bash
+yq eval '.a anchor |= .b' sample.yml
+```
+will output
+```yaml
+a: &cat
+  b: cat
+```
+
+## Get alias
+Given a sample.yml file of:
+```yaml
+b: &billyBob meow
+a: *billyBob
+```
+then
+```bash
+yq eval '.a | alias' sample.yml
+```
+will output
+```yaml
+billyBob
+```
+
+## Set alias
+Given a sample.yml file of:
+```yaml
+b: &meow purr
+a: cat
+```
+then
+```bash
+yq eval '.a alias = "meow"' sample.yml
+```
+will output
+```yaml
+b: &meow purr
+a: *meow
+```
+
+## Set alias to blank does nothing
+Given a sample.yml file of:
+```yaml
+b: &meow purr
+a: cat
+```
+then
+```bash
+yq eval '.a alias = ""' sample.yml
+```
+will output
+```yaml
+b: &meow purr
+a: cat
+```
+
+## Set alias relatively using assign-update
+Given a sample.yml file of:
+```yaml
+b: &meow purr
+a:
+  f: meow
+```
+then
+```bash
+yq eval '.a alias |= .f' sample.yml
+```
+will output
+```yaml
+b: &meow purr
+a: *meow
+```
+
+## Explode alias and anchor
+Given a sample.yml file of:
+```yaml
+f:
+  a: &a cat
+  b: *a
+```
+then
+```bash
+yq eval 'explode(.f)' sample.yml
+```
+will output
+```yaml
+f:
+  a: cat
+  b: cat
+```
+
+## Explode with no aliases or anchors
+Given a sample.yml file of:
+```yaml
+a: mike
+```
+then
+```bash
+yq eval 'explode(.a)' sample.yml
+```
+will output
+```yaml
+a: mike
+```
+
+## Explode with alias keys
+Given a sample.yml file of:
+```yaml
+f:
+  a: &a cat
+  *a: b
+```
+then
+```bash
+yq eval 'explode(.f)' sample.yml
+```
+will output
+```yaml
+f:
+  a: cat
+  cat: b
+```
+
+## Explode with merge anchors
+Given a sample.yml file of:
+```yaml
+foo: &foo
+  a: foo_a
+  thing: foo_thing
+  c: foo_c
+bar: &bar
+  b: bar_b
+  thing: bar_thing
+  c: bar_c
+foobarList:
+  b: foobarList_b
+  !!merge <<:
+    - *foo
+    - *bar
+  c: foobarList_c
+foobar:
+  c: foobar_c
+  !!merge <<: *foo
+  thing: foobar_thing
+```
+then
+```bash
+yq eval 'explode(.)' sample.yml
+```
+will output
+```yaml
+foo:
+  a: foo_a
+  thing: foo_thing
+  c: foo_c
+bar:
+  b: bar_b
+  thing: bar_thing
+  c: bar_c
+foobarList:
+  b: bar_b
+  thing: foo_thing
+  c: foobarList_c
+  a: foo_a
+foobar:
+  c: foo_c
+  a: foo_a
+  thing: foobar_thing
+```
+

pkg/yqlib/doc/Assign (Update).md

@@ -1,10 +1,4 @@
-This operator is used to update node values. It can be used in either the:
 
-### plain form: `=`
-Which will assign the LHS node values to the RHS node values. The RHS expression is run against the matching nodes in the pipeline.
-
-### relative form: `|=`
-This will do a similar thing to the plain form, however, the RHS expression is run against _the LHS nodes_. This is useful for updating values based on old values, e.g. increment.
 ## Create yaml file
 Running
 ```bash
@@ -34,6 +28,27 @@ a:
   g: foof
 ```
 
+## Update node from another file
+Note this will also work when the second file is a scalar (string/number)
+
+Given a sample.yml file of:
+```yaml
+a: apples
+```
+And another sample another.yml file of:
+```yaml
+b: bob
+```
+then
+```bash
+yq eval-all 'select(fileIndex==0).a = select(fileIndex==1) | select(fileIndex==0)' sample.yml another.yml
+```
+will output
+```yaml
+a:
+  b: bob
+```
+
 ## Update node to be the sibling value
 Given a sample.yml file of:
 ```yaml
@@ -112,7 +127,7 @@ a:
 ```
 then
 ```bash
-yq eval '(.a.[] | select(. == "apple")) = "frog"' sample.yml
+yq eval '(.a[] | select(. == "apple")) = "frog"' sample.yml
 ```
 will output
 ```yaml

pkg/yqlib/doc/Boolean Operators.md

@@ -1,5 +1,14 @@
-The `or` and `and` operators take two parameters and return a boolean result. `not` flips a boolean from true to false, or vice versa. These are most commonly used with the `select` operator to filter particular nodes.
-## OR example
+The `or` and `and` operators take two parameters and return a boolean result. 
+
+`not` flips a boolean from true to false, or vice versa. 
+
+`any` will return `true` if there are any `true` values in a array sequence, and `all` will return true if _all_ elements in an array are true.
+
+`any_c(condition)` and `all_c(condition)` are like `any` and `all` but they take a condition expression that is used against each element to determine if it's `true`. Note: in `jq` you can simply pass a condition to `any` or `all` and it simply works - `yq` isn't that clever..yet
+
+These are most commonly used with the `select` operator to filter particular nodes.
+
+## `or` example
 Running
 ```bash
 yq eval --null-input 'true or false'
@@ -9,7 +18,7 @@ will output
 true
 ```
 
-## AND example
+## `and` example
 Running
 ```bash
 yq eval --null-input 'true and false'
@@ -41,6 +50,104 @@ will output
   b: fly
 ```
 
+## `any` returns true if any boolean in a given array is true
+Given a sample.yml file of:
+```yaml
+- false
+- true
+```
+then
+```bash
+yq eval 'any' sample.yml
+```
+will output
+```yaml
+true
+```
+
+## `any` returns false for an empty array
+Given a sample.yml file of:
+```yaml
+[]
+```
+then
+```bash
+yq eval 'any' sample.yml
+```
+will output
+```yaml
+false
+```
+
+## `any_c` returns true if any element in the array is true for the given condition.
+Given a sample.yml file of:
+```yaml
+a:
+  - rad
+  - awesome
+b:
+  - meh
+  - whatever
+```
+then
+```bash
+yq eval '.[] |= any_c(. == "awesome")' sample.yml
+```
+will output
+```yaml
+a: true
+b: false
+```
+
+## `all` returns true if all booleans in a given array are true
+Given a sample.yml file of:
+```yaml
+- true
+- true
+```
+then
+```bash
+yq eval 'all' sample.yml
+```
+will output
+```yaml
+true
+```
+
+## `all` returns true for an empty array
+Given a sample.yml file of:
+```yaml
+[]
+```
+then
+```bash
+yq eval 'all' sample.yml
+```
+will output
+```yaml
+true
+```
+
+## `all_c` returns true if all elements in the array are true for the given condition.
+Given a sample.yml file of:
+```yaml
+a:
+  - rad
+  - awesome
+b:
+  - meh
+  - 12
+```
+then
+```bash
+yq eval '.[] |= all_c(tag == "!!str")' sample.yml
+```
+will output
+```yaml
+a: true
+b: false
+```
+
 ## Not true is false
 Running
 ```bash

pkg/yqlib/doc/Comment Operators.md

@@ -1,4 +1,15 @@
 Use these comment operators to set or retrieve comments.
+
+Like the `=` and `|=` assign operators, the same syntax applies when updating comments:
+
+
+### plain form: `=`
+This will assign the LHS nodes comments to the expression on the RHS. The RHS is run against the matching nodes in the pipeline
+
+### relative form: `|=` 
+Similar to the plain form, however the RHS evaluates against each matching LHS node! This is useful if you want to set the comments as a relative expression of the node, for instance its value or path.
+
+
 ## Set line comment
 Given a sample.yml file of:
 ```yaml
@@ -13,6 +24,22 @@ will output
 a: cat # single
 ```
 
+## Use update assign to perform relative updates
+Given a sample.yml file of:
+```yaml
+a: cat
+b: dog
+```
+then
+```bash
+yq eval '.. lineComment |= .' sample.yml
+```
+will output
+```yaml
+a: cat # cat
+b: dog # dog
+```
+
 ## Set head comment
 Given a sample.yml file of:
 ```yaml
@@ -61,18 +88,23 @@ a: cat
 b: dog # leave this
 ```
 
-## Remove all comments
+## Remove (strip) all comments
+Note the use of `...` to ensure key nodes are included.
+
 Given a sample.yml file of:
 ```yaml
 a: cat # comment
+# great
+b: # key comment
 ```
 then
 ```bash
-yq eval '.. comments=""' sample.yml
+yq eval '... comments=""' sample.yml
 ```
 will output
 ```yaml
 a: cat
+b:
 ```
 
 ## Get line comment

pkg/yqlib/doc/Delete.md

@@ -14,6 +14,23 @@ will output
 a: cat
 ```
 
+## Delete nested entry in map
+Given a sample.yml file of:
+```yaml
+a:
+  a1: fred
+  a2: frood
+```
+then
+```bash
+yq eval 'del(.a.a1)' sample.yml
+```
+will output
+```yaml
+a:
+  a2: frood
+```
+
 ## Delete entry in array
 Given a sample.yml file of:
 ```yaml
@@ -31,6 +48,21 @@ will output
 - 3
 ```
 
+## Delete nested entry in array
+Given a sample.yml file of:
+```yaml
+- a: cat
+  b: dog
+```
+then
+```bash
+yq eval 'del(.[0].a)' sample.yml
+```
+will output
+```yaml
+- b: dog
+```
+
 ## Delete no matches
 Given a sample.yml file of:
 ```yaml
@@ -63,3 +95,23 @@ will output
 b: dog
 ```
 
+## Recursively delete matching keys
+Given a sample.yml file of:
+```yaml
+a:
+  name: frog
+  b:
+    name: blog
+    age: 12
+```
+then
+```bash
+yq eval 'del(.. | select(has("name")).name)' sample.yml
+```
+will output
+```yaml
+a:
+  b:
+    age: 12
+```
+

pkg/yqlib/doc/Document Index.md

@@ -1,4 +1,4 @@
-Use the `documentIndex` operator to select nodes of a particular document.
+Use the `documentIndex` operator (or the `di` shorthand) to select nodes of a particular document.
 ## Retrieve a document index
 Given a sample.yml file of:
 ```yaml
@@ -17,6 +17,24 @@ will output
 1
 ```
 
+## Retrieve a document index, shorthand
+Given a sample.yml file of:
+```yaml
+a: cat
+---
+a: frog
+```
+then
+```bash
+yq eval '.a | di' sample.yml
+```
+will output
+```yaml
+0
+---
+1
+```
+
 ## Filter by document index
 Given a sample.yml file of:
 ```yaml
@@ -26,7 +44,23 @@ a: frog
 ```
 then
 ```bash
-yq eval 'select(. | documentIndex == 1)' sample.yml
+yq eval 'select(documentIndex == 1)' sample.yml
+```
+will output
+```yaml
+a: frog
+```
+
+## Filter by document index shorthand
+Given a sample.yml file of:
+```yaml
+a: cat
+---
+a: frog
+```
+then
+```bash
+yq eval 'select(di == 1)' sample.yml
 ```
 will output
 ```yaml
@@ -42,7 +76,7 @@ a: frog
 ```
 then
 ```bash
-yq eval '.a | ({"match": ., "doc": (. | documentIndex)})' sample.yml
+yq eval '.a | ({"match": ., "doc": documentIndex})' sample.yml
 ```
 will output
 ```yaml

pkg/yqlib/doc/Entries.md

@@ -0,0 +1,100 @@
+Similar to the same named functions in `jq` these functions convert to/from an object and an array of key-value pairs. This is most useful for performing operations on keys of maps.
+## to_entries Map
+Given a sample.yml file of:
+```yaml
+a: 1
+b: 2
+```
+then
+```bash
+yq eval 'to_entries' sample.yml
+```
+will output
+```yaml
+- key: a
+  value: 1
+- key: b
+  value: 2
+```
+
+## to_entries Array
+Given a sample.yml file of:
+```yaml
+- a
+- b
+```
+then
+```bash
+yq eval 'to_entries' sample.yml
+```
+will output
+```yaml
+- key: 0
+  value: a
+- key: 1
+  value: b
+```
+
+## to_entries null
+Given a sample.yml file of:
+```yaml
+null
+```
+then
+```bash
+yq eval 'to_entries' sample.yml
+```
+will output
+```yaml
+```
+
+## from_entries map
+Given a sample.yml file of:
+```yaml
+a: 1
+b: 2
+```
+then
+```bash
+yq eval 'to_entries | from_entries' sample.yml
+```
+will output
+```yaml
+a: 1
+b: 2
+```
+
+## from_entries with numeric key indexes
+from_entries always creates a map, even for numeric keys
+
+Given a sample.yml file of:
+```yaml
+- a
+- b
+```
+then
+```bash
+yq eval 'to_entries | from_entries' sample.yml
+```
+will output
+```yaml
+0: a
+1: b
+```
+
+## Use with_entries to update keys
+Given a sample.yml file of:
+```yaml
+a: 1
+b: 2
+```
+then
+```bash
+yq eval 'with_entries(.key |= "KEY_" + .)' sample.yml
+```
+will output
+```yaml
+KEY_a: 1
+KEY_b: 2
+```
+

pkg/yqlib/doc/Env Variable Operators.md

@@ -0,0 +1,78 @@
+This operator is used to handle environment variables usage in path expressions. While environment variables can, of course, be passed in via your CLI with string interpolation, this often comes with complex quote escaping and can be tricky to write and read. Note that there are two forms, `env` which will parse the environment variable as a yaml (be it a map, array, string, number of boolean) and `strenv` which will always parse the argument as a string.
+
+
+## Read string environment variable
+Running
+```bash
+myenv="cat meow" yq eval --null-input '.a = env(myenv)'
+```
+will output
+```yaml
+a: cat meow
+```
+
+## Read boolean environment variable
+Running
+```bash
+myenv="true" yq eval --null-input '.a = env(myenv)'
+```
+will output
+```yaml
+a: true
+```
+
+## Read numeric environment variable
+Running
+```bash
+myenv="12" yq eval --null-input '.a = env(myenv)'
+```
+will output
+```yaml
+a: 12
+```
+
+## Read yaml environment variable
+Running
+```bash
+myenv="{b: fish}" yq eval --null-input '.a = env(myenv)'
+```
+will output
+```yaml
+a: {b: fish}
+```
+
+## Read boolean environment variable as a string
+Running
+```bash
+myenv="true" yq eval --null-input '.a = strenv(myenv)'
+```
+will output
+```yaml
+a: "true"
+```
+
+## Read numeric environment variable as a string
+Running
+```bash
+myenv="12" yq eval --null-input '.a = strenv(myenv)'
+```
+will output
+```yaml
+a: "12"
+```
+
+## Dynamic key lookup with environment variable
+Given a sample.yml file of:
+```yaml
+cat: meow
+dog: woof
+```
+then
+```bash
+myenv="cat" yq eval '.[env(myenv)]' sample.yml
+```
+will output
+```yaml
+meow
+```
+

pkg/yqlib/doc/Equals.md

@@ -29,6 +29,24 @@ true
 false
 ```
 
+## Don't match string
+Given a sample.yml file of:
+```yaml
+- cat
+- goat
+- dog
+```
+then
+```bash
+yq eval '.[] | (. != "*at")' sample.yml
+```
+will output
+```yaml
+false
+false
+true
+```
+
 ## Match number
 Given a sample.yml file of:
 ```yaml
@@ -47,6 +65,24 @@ true
 false
 ```
 
+## Dont match number
+Given a sample.yml file of:
+```yaml
+- 3
+- 4
+- 5
+```
+then
+```bash
+yq eval '.[] | (. != 4)' sample.yml
+```
+will output
+```yaml
+true
+false
+true
+```
+
 ## Match nulls
 Running
 ```bash
@@ -57,3 +93,31 @@ will output
 true
 ```
 
+## Non exisitant key doesn't equal a value
+Given a sample.yml file of:
+```yaml
+a: frog
+```
+then
+```bash
+yq eval 'select(.b != "thing")' sample.yml
+```
+will output
+```yaml
+a: frog
+```
+
+## Two non existant keys are equal
+Given a sample.yml file of:
+```yaml
+a: frog
+```
+then
+```bash
+yq eval 'select(.b == .c)' sample.yml
+```
+will output
+```yaml
+a: frog
+```
+

pkg/yqlib/doc/Explode.md

@@ -1,98 +0,0 @@
-Explodes (or dereferences) aliases and anchors.
-## Explode alias and anchor
-Given a sample.yml file of:
-```yaml
-f:
-  a: &a cat
-  b: *a
-```
-then
-```bash
-yq eval 'explode(.f)' sample.yml
-```
-will output
-```yaml
-f:
-  a: cat
-  b: cat
-```
-
-## Explode with no aliases or anchors
-Given a sample.yml file of:
-```yaml
-a: mike
-```
-then
-```bash
-yq eval 'explode(.a)' sample.yml
-```
-will output
-```yaml
-a: mike
-```
-
-## Explode with alias keys
-Given a sample.yml file of:
-```yaml
-f:
-  a: &a cat
-  *a: b
-```
-then
-```bash
-yq eval 'explode(.f)' sample.yml
-```
-will output
-```yaml
-f:
-  a: cat
-  cat: b
-```
-
-## Explode with merge anchors
-Given a sample.yml file of:
-```yaml
-foo: &foo
-  a: foo_a
-  thing: foo_thing
-  c: foo_c
-bar: &bar
-  b: bar_b
-  thing: bar_thing
-  c: bar_c
-foobarList:
-  b: foobarList_b
-  !!merge <<:
-    - *foo
-    - *bar
-  c: foobarList_c
-foobar:
-  c: foobar_c
-  !!merge <<: *foo
-  thing: foobar_thing
-```
-then
-```bash
-yq eval 'explode(.)' sample.yml
-```
-will output
-```yaml
-foo:
-  a: foo_a
-  thing: foo_thing
-  c: foo_c
-bar:
-  b: bar_b
-  thing: bar_thing
-  c: bar_c
-foobarList:
-  b: bar_b
-  a: foo_a
-  thing: bar_thing
-  c: foobarList_c
-foobar:
-  c: foo_c
-  a: foo_a
-  thing: foobar_thing
-```
-

pkg/yqlib/doc/File Operators.md

@@ -1,9 +1,11 @@
 File operators are most often used with merge when needing to merge specific files together. Note that when doing this, you will need to use `eval-all` to ensure all yaml documents are loaded into memory before performing the merge (as opposed to `eval` which runs the expression once per document).
 
+Note that the `fileIndex` operator has a short alias of `fi`.
+
 ## Merging files
 Note the use of eval-all to ensure all documents are loaded into memory.
 ```bash
-yq eval-all 'select(fileIndex == 0) * select(filename == "file2.yaml")' file1.yaml file2.yaml
+yq eval-all 'select(fi == 0) * select(filename == "file2.yaml")' file1.yaml file2.yaml
 ```
 ## Get filename
 Given a sample.yml file of:
@@ -16,7 +18,7 @@ yq eval 'filename' sample.yml
 ```
 will output
 ```yaml
-sample.yaml
+sample.yml
 ```
 
 ## Get file index
@@ -33,3 +35,37 @@ will output
 0
 ```
 
+## Get file indices of multiple documents
+Given a sample.yml file of:
+```yaml
+a: cat
+```
+And another sample another.yml file of:
+```yaml
+a: cat
+```
+then
+```bash
+yq eval-all 'fileIndex' sample.yml another.yml
+```
+will output
+```yaml
+0
+---
+1
+```
+
+## Get file index alias
+Given a sample.yml file of:
+```yaml
+a: cat
+```
+then
+```bash
+yq eval 'fi' sample.yml
+```
+will output
+```yaml
+0
+```
+

pkg/yqlib/doc/Has.md

@@ -19,6 +19,29 @@ true
 false
 ```
 
+## Select, checking for existence of deep paths
+Simply pipe in parent expressions into `has`
+
+Given a sample.yml file of:
+```yaml
+- a:
+    b:
+      c: cat
+- a:
+    b:
+      d: dog
+```
+then
+```bash
+yq eval '.[] | select(.a.b | has("c"))' sample.yml
+```
+will output
+```yaml
+a:
+  b:
+    c: cat
+```
+
 ## Has array index
 Given a sample.yml file of:
 ```yaml

pkg/yqlib/doc/Keys.md

@@ -0,0 +1,35 @@
+# Keys
+
+Use the `keys` operator to return map keys or array indices. 
+## Map keys
+Given a sample.yml file of:
+```yaml
+dog: woof
+cat: meow
+```
+then
+```bash
+yq eval 'keys' sample.yml
+```
+will output
+```yaml
+- dog
+- cat
+```
+
+## Array keys
+Given a sample.yml file of:
+```yaml
+- apple
+- banana
+```
+then
+```bash
+yq eval 'keys' sample.yml
+```
+will output
+```yaml
+- 0
+- 1
+```
+

pkg/yqlib/doc/Length.md

@@ -16,6 +16,20 @@ will output
 3
 ```
 
+## null length
+Given a sample.yml file of:
+```yaml
+a: null
+```
+then
+```bash
+yq eval '.a | length' sample.yml
+```
+will output
+```yaml
+0
+```
+
 ## Map length
 returns number of entries
 

pkg/yqlib/doc/Multiply (Merge).md

@@ -0,0 +1,366 @@
+Like the multiple operator in jq, depending on the operands, this multiply operator will do different things. Currently numbers, arrays and objects are supported.
+
+## Objects and arrays - merging
+Objects are merged deeply matching on matching keys. By default, array values override and are not deeply merged.
+
+Note that when merging objects, this operator returns the merged object (not the parent). This will be clearer in the examples below.
+
+### Merge Flags
+You can control how objects are merged by using one or more of the following flags. Multiple flags can be used together, e.g. `.a *+? .b`.  See examples below
+
+- `+` to append arrays
+- `?` to only merge existing fields
+- `d` to deeply merge arrays
+
+### Merging files
+Note the use of `eval-all` to ensure all documents are loaded into memory.
+
+```bash
+yq eval-all 'select(fileIndex == 0) * select(fileIndex == 1)' file1.yaml file2.yaml
+```
+
+## Multiply integers
+Running
+```bash
+yq eval --null-input '3 * 4'
+```
+will output
+```yaml
+12
+```
+
+## Merge objects together, returning merged result only
+Given a sample.yml file of:
+```yaml
+a:
+  field: me
+  fieldA: cat
+b:
+  field:
+    g: wizz
+  fieldB: dog
+```
+then
+```bash
+yq eval '.a * .b' sample.yml
+```
+will output
+```yaml
+field:
+  g: wizz
+fieldA: cat
+fieldB: dog
+```
+
+## Merge objects together, returning parent object
+Given a sample.yml file of:
+```yaml
+a:
+  field: me
+  fieldA: cat
+b:
+  field:
+    g: wizz
+  fieldB: dog
+```
+then
+```bash
+yq eval '. * {"a":.b}' sample.yml
+```
+will output
+```yaml
+a:
+  field:
+    g: wizz
+  fieldA: cat
+  fieldB: dog
+b:
+  field:
+    g: wizz
+  fieldB: dog
+```
+
+## Merge keeps style of LHS
+Given a sample.yml file of:
+```yaml
+a: {things: great}
+b:
+  also: "me"
+```
+then
+```bash
+yq eval '. * {"a":.b}' sample.yml
+```
+will output
+```yaml
+a: {things: great, also: "me"}
+b:
+  also: "me"
+```
+
+## Merge arrays
+Given a sample.yml file of:
+```yaml
+a:
+  - 1
+  - 2
+  - 3
+b:
+  - 3
+  - 4
+  - 5
+```
+then
+```bash
+yq eval '. * {"a":.b}' sample.yml
+```
+will output
+```yaml
+a:
+  - 3
+  - 4
+  - 5
+b:
+  - 3
+  - 4
+  - 5
+```
+
+## Merge, only existing fields
+Given a sample.yml file of:
+```yaml
+a:
+  thing: one
+  cat: frog
+b:
+  missing: two
+  thing: two
+```
+then
+```bash
+yq eval '.a *? .b' sample.yml
+```
+will output
+```yaml
+thing: two
+cat: frog
+```
+
+## Merge, appending arrays
+Given a sample.yml file of:
+```yaml
+a:
+  array:
+    - 1
+    - 2
+    - animal: dog
+  value: coconut
+b:
+  array:
+    - 3
+    - 4
+    - animal: cat
+  value: banana
+```
+then
+```bash
+yq eval '.a *+ .b' sample.yml
+```
+will output
+```yaml
+array:
+  - 1
+  - 2
+  - animal: dog
+  - 3
+  - 4
+  - animal: cat
+value: banana
+```
+
+## Merge, only existing fields, appending arrays
+Given a sample.yml file of:
+```yaml
+a:
+  thing:
+    - 1
+    - 2
+b:
+  thing:
+    - 3
+    - 4
+  another:
+    - 1
+```
+then
+```bash
+yq eval '.a *?+ .b' sample.yml
+```
+will output
+```yaml
+thing:
+  - 1
+  - 2
+  - 3
+  - 4
+```
+
+## Merge, deeply merging arrays
+Merging arrays deeply means arrays are merge like objects, with indexes as their key. In this case, we merge the first item in the array, and do nothing with the second.
+
+Given a sample.yml file of:
+```yaml
+a:
+  - name: fred
+    age: 12
+  - name: bob
+    age: 32
+b:
+  - name: fred
+    age: 34
+```
+then
+```bash
+yq eval '.a *d .b' sample.yml
+```
+will output
+```yaml
+- name: fred
+  age: 34
+- name: bob
+  age: 32
+```
+
+## Merge arrays of objects together, matching on a key
+It's a complex command, the trickyness comes from needing to have the right context in the expressions.
+First we save the second array into a variable '$two' which lets us reference it later.
+We then need to update the first array. We will use the relative update (|=) because we need to update relative to the current element of the array in the LHS in the RHS expression. 
+We set the current element of the first array as $cur. Now we multiply (merge) $cur with the matching entry in $two, by passing $two through a select filter.
+
+
+Given a sample.yml file of:
+```yaml
+- a: apple
+  b: appleB
+- a: kiwi
+  b: kiwiB
+- a: banana
+  b: bananaB
+```
+And another sample another.yml file of:
+```yaml
+- a: banana
+  c: bananaC
+- a: apple
+  b: appleB2
+- a: dingo
+  c: dingoC
+```
+then
+```bash
+yq eval-all '(select(fi==1) | .[]) as $two | select(fi==0) | .[] |= (. as $cur |  $cur * ($two | select(.a == $cur.a)))' sample.yml another.yml
+```
+will output
+```yaml
+- a: apple
+  b: appleB2
+- a: kiwi
+  b: kiwiB
+- a: banana
+  b: bananaB
+  c: bananaC
+```
+
+## Merge to prefix an element
+Given a sample.yml file of:
+```yaml
+a: cat
+b: dog
+```
+then
+```bash
+yq eval '. * {"a": {"c": .a}}' sample.yml
+```
+will output
+```yaml
+a:
+  c: cat
+b: dog
+```
+
+## Merge with simple aliases
+Given a sample.yml file of:
+```yaml
+a: &cat
+  c: frog
+b:
+  f: *cat
+c:
+  g: thongs
+```
+then
+```bash
+yq eval '.c * .b' sample.yml
+```
+will output
+```yaml
+g: thongs
+f: *cat
+```
+
+## Merge copies anchor names
+Given a sample.yml file of:
+```yaml
+a:
+  c: &cat frog
+b:
+  f: *cat
+c:
+  g: thongs
+```
+then
+```bash
+yq eval '.c * .a' sample.yml
+```
+will output
+```yaml
+g: thongs
+c: &cat frog
+```
+
+## Merge with merge anchors
+Given a sample.yml file of:
+```yaml
+foo: &foo
+  a: foo_a
+  thing: foo_thing
+  c: foo_c
+bar: &bar
+  b: bar_b
+  thing: bar_thing
+  c: bar_c
+foobarList:
+  b: foobarList_b
+  !!merge <<:
+    - *foo
+    - *bar
+  c: foobarList_c
+foobar:
+  c: foobar_c
+  !!merge <<: *foo
+  thing: foobar_thing
+```
+then
+```bash
+yq eval '.foobar * .foobarList' sample.yml
+```
+will output
+```yaml
+c: foobarList_c
+<<:
+  - *foo
+  - *bar
+thing: foobar_thing
+b: foobarList_b
+```
+

pkg/yqlib/doc/Multiply.md

@@ -1,238 +0,0 @@
-Like the multiple operator in `jq`, depending on the operands, this multiply operator will do different things. Currently only objects are supported, which have the effect of merging the RHS into the LHS.
-
-Upcoming versions of `yq` will add support for other types of multiplication (numbers, strings).
-
-To concatenate when merging objects, use the `*+` form (see examples below). This will recursively merge objects, appending arrays when it encounters them.
-
-Note that when merging objects, this operator returns the merged object (not the parent). This will be clearer in the examples below.
-
-## Merging files
-Note the use of eval-all to ensure all documents are loaded into memory.
-
-```bash
-yq eval-all 'select(fileIndex == 0) * select(fileIndex == 1)' file1.yaml file2.yaml
-```
-
-## Merge objects together, returning merged result only
-Given a sample.yml file of:
-```yaml
-a:
-  field: me
-  fieldA: cat
-b:
-  field:
-    g: wizz
-  fieldB: dog
-```
-then
-```bash
-yq eval '.a * .b' sample.yml
-```
-will output
-```yaml
-field:
-  g: wizz
-fieldA: cat
-fieldB: dog
-```
-
-## Merge objects together, returning parent object
-Given a sample.yml file of:
-```yaml
-a:
-  field: me
-  fieldA: cat
-b:
-  field:
-    g: wizz
-  fieldB: dog
-```
-then
-```bash
-yq eval '. * {"a":.b}' sample.yml
-```
-will output
-```yaml
-a:
-  field:
-    g: wizz
-  fieldA: cat
-  fieldB: dog
-b:
-  field:
-    g: wizz
-  fieldB: dog
-```
-
-## Merge keeps style of LHS
-Given a sample.yml file of:
-```yaml
-a: {things: great}
-b:
-  also: "me"
-
-```
-then
-```bash
-yq eval '. * {"a":.b}' sample.yml
-```
-will output
-```yaml
-a: {things: great, also: "me"}
-b:
-  also: "me"
-```
-
-## Merge arrays
-Given a sample.yml file of:
-```yaml
-a:
-  - 1
-  - 2
-  - 3
-b:
-  - 3
-  - 4
-  - 5
-```
-then
-```bash
-yq eval '. * {"a":.b}' sample.yml
-```
-will output
-```yaml
-a:
-  - 3
-  - 4
-  - 5
-b:
-  - 3
-  - 4
-  - 5
-```
-
-## Merge, appending arrays
-Given a sample.yml file of:
-```yaml
-a:
-  array:
-    - 1
-    - 2
-    - animal: dog
-  value: coconut
-b:
-  array:
-    - 3
-    - 4
-    - animal: cat
-  value: banana
-```
-then
-```bash
-yq eval '.a *+ .b' sample.yml
-```
-will output
-```yaml
-array:
-  - 1
-  - 2
-  - animal: dog
-  - 3
-  - 4
-  - animal: cat
-value: banana
-```
-
-## Merge to prefix an element
-Given a sample.yml file of:
-```yaml
-a: cat
-b: dog
-```
-then
-```bash
-yq eval '. * {"a": {"c": .a}}' sample.yml
-```
-will output
-```yaml
-a:
-  c: cat
-b: dog
-```
-
-## Merge with simple aliases
-Given a sample.yml file of:
-```yaml
-a: &cat
-  c: frog
-b:
-  f: *cat
-c:
-  g: thongs
-```
-then
-```bash
-yq eval '.c * .b' sample.yml
-```
-will output
-```yaml
-g: thongs
-f: *cat
-```
-
-## Merge does not copy anchor names
-Given a sample.yml file of:
-```yaml
-a:
-  c: &cat frog
-b:
-  f: *cat
-c:
-  g: thongs
-```
-then
-```bash
-yq eval '.c * .a' sample.yml
-```
-will output
-```yaml
-g: thongs
-c: frog
-```
-
-## Merge with merge anchors
-Given a sample.yml file of:
-```yaml
-foo: &foo
-  a: foo_a
-  thing: foo_thing
-  c: foo_c
-bar: &bar
-  b: bar_b
-  thing: bar_thing
-  c: bar_c
-foobarList:
-  b: foobarList_b
-  !!merge <<:
-    - *foo
-    - *bar
-  c: foobarList_c
-foobar:
-  c: foobar_c
-  !!merge <<: *foo
-  thing: foobar_thing
-```
-then
-```bash
-yq eval '.foobar * .foobarList' sample.yml
-```
-will output
-```yaml
-c: foobarList_c
-<<:
-  - *foo
-  - *bar
-thing: foobar_thing
-b: foobarList_b
-```
-

pkg/yqlib/doc/Recursive Descent (Glob).md

@@ -0,0 +1,154 @@
+This operator recursively matches (or globs) all children nodes given of a particular element, including that node itself. This is most often used to apply a filter recursively against all matches. It can be used in either the 
+
+## match values form `..`
+This will, like the `jq` equivalent, recursively match all _value_ nodes. Use it to find/manipulate particular values.
+
+For instance to set the `style` of all _value_ nodes in a yaml doc, excluding map keys:
+
+```bash
+yq eval '.. style= "flow"' file.yaml
+```
+
+## match values and map keys form `...`
+The also includes map keys in the results set. This is particularly useful in YAML as unlike JSON, map keys can have their own styling, tags and use anchors and aliases.
+
+For instance to set the `style` of all nodes in a yaml doc, including the map keys:
+
+```bash
+yq eval '... style= "flow"' file.yaml
+```
+## Recurse map (values only)
+Given a sample.yml file of:
+```yaml
+a: frog
+```
+then
+```bash
+yq eval '..' sample.yml
+```
+will output
+```yaml
+a: frog
+frog
+```
+
+## Recursively find nodes with keys
+Note that this example has wrapped the expression in `[]` to show that there are two matches returned. You do not have to wrap in `[]` in your path expression.
+
+Given a sample.yml file of:
+```yaml
+a:
+  name: frog
+  b:
+    name: blog
+    age: 12
+```
+then
+```bash
+yq eval '[.. | select(has("name"))]' sample.yml
+```
+will output
+```yaml
+- name: frog
+  b:
+    name: blog
+    age: 12
+- name: blog
+  age: 12
+```
+
+## Recursively find nodes with values
+Given a sample.yml file of:
+```yaml
+a:
+  nameA: frog
+  b:
+    nameB: frog
+    age: 12
+```
+then
+```bash
+yq eval '.. | select(. == "frog")' sample.yml
+```
+will output
+```yaml
+frog
+frog
+```
+
+## Recurse map (values and keys)
+Note that the map key appears in the results
+
+Given a sample.yml file of:
+```yaml
+a: frog
+```
+then
+```bash
+yq eval '...' sample.yml
+```
+will output
+```yaml
+a: frog
+a
+frog
+```
+
+## Aliases are not traversed
+Given a sample.yml file of:
+```yaml
+a: &cat
+  c: frog
+b: *cat
+```
+then
+```bash
+yq eval '[..]' sample.yml
+```
+will output
+```yaml
+- a: &cat
+    c: frog
+  b: *cat
+- &cat
+  c: frog
+- frog
+- *cat
+```
+
+## Merge docs are not traversed
+Given a sample.yml file of:
+```yaml
+foo: &foo
+  a: foo_a
+  thing: foo_thing
+  c: foo_c
+bar: &bar
+  b: bar_b
+  thing: bar_thing
+  c: bar_c
+foobarList:
+  b: foobarList_b
+  !!merge <<:
+    - *foo
+    - *bar
+  c: foobarList_c
+foobar:
+  c: foobar_c
+  !!merge <<: *foo
+  thing: foobar_thing
+```
+then
+```bash
+yq eval '.foobar | [..]' sample.yml
+```
+will output
+```yaml
+- c: foobar_c
+  !!merge <<: *foo
+  thing: foobar_thing
+- foobar_c
+- *foo
+- foobar_thing
+```
+

pkg/yqlib/doc/Recursive Descent.md

@@ -1,63 +0,0 @@
-This operator recursively matches all children nodes given of a particular element, including that node itself. This is most often used to apply a filter recursively against all matches, for instance to set the `style` of all nodes in a yaml doc:
-
-```bash
-yq eval '.. style= "flow"' file.yaml
-```
-## Aliases are not traversed
-Given a sample.yml file of:
-```yaml
-a: &cat
-  c: frog
-b: *cat
-```
-then
-```bash
-yq eval '[..]' sample.yml
-```
-will output
-```yaml
-- a: &cat
-    c: frog
-  b: *cat
-- &cat
-  c: frog
-- frog
-- *cat
-```
-
-## Merge docs are not traversed
-Given a sample.yml file of:
-```yaml
-foo: &foo
-  a: foo_a
-  thing: foo_thing
-  c: foo_c
-bar: &bar
-  b: bar_b
-  thing: bar_thing
-  c: bar_c
-foobarList:
-  b: foobarList_b
-  !!merge <<:
-    - *foo
-    - *bar
-  c: foobarList_c
-foobar:
-  c: foobar_c
-  !!merge <<: *foo
-  thing: foobar_thing
-```
-then
-```bash
-yq eval '.foobar | [..]' sample.yml
-```
-will output
-```yaml
-- c: foobar_c
-  !!merge <<: *foo
-  thing: foobar_thing
-- foobar_c
-- *foo
-- foobar_thing
-```
-

pkg/yqlib/doc/Reduce.md

@@ -0,0 +1,76 @@
+Reduce is a powerful way to process a collection of data into a new form.
+
+```
+<exp> as $<name> ireduce (<init>; <block>)
+```
+
+e.g.
+
+```
+.[] as $item ireduce (0; . + $item)
+```
+
+On the LHS we are configuring the collection of items that will be reduced `<exp>` as well as what each element will be called `$<name>`. Note that the array has been splatted into its individual elements.
+
+On the RHS there is `<init>`, the starting value of the accumulator and `<block>`, the expression that will update the accumulator for each element in the collection. Note that within the block expression, `.` will evaluate to the current value of the accumulator. 
+
+## yq vs jq syntax
+Reduce syntax in `yq` is a little different from `jq` - as `yq` (currently) isn't as sophisticated as `jq` and its only supports infix notation (e.g. a + b, where the operator is in the middle of the two parameters) - where as `jq` uses a mix of infix notation with _prefix_ notation (e.g. `reduce a b` is like writing `+ a b`).
+
+To that end, the reduce operator is called `ireduce` for backwards compatability if a `jq` like prefix version of `reduce` is ever added.
+
+
+## Sum numbers
+Given a sample.yml file of:
+```yaml
+- 10
+- 2
+- 5
+- 3
+```
+then
+```bash
+yq eval '.[] as $item ireduce (0; . + $item)' sample.yml
+```
+will output
+```yaml
+20
+```
+
+## Merge all yaml files together
+Given a sample.yml file of:
+```yaml
+a: cat
+```
+And another sample another.yml file of:
+```yaml
+b: dog
+```
+then
+```bash
+yq eval-all '. as $item ireduce ({}; . * $item )' sample.yml another.yml
+```
+will output
+```yaml
+a: cat
+b: dog
+```
+
+## Convert an array to an object
+Given a sample.yml file of:
+```yaml
+- name: Cathy
+  has: apples
+- name: Bob
+  has: bananas
+```
+then
+```bash
+yq eval '.[] as $item ireduce ({}; .[$item | .name] = ($item | .has) )' sample.yml
+```
+will output
+```yaml
+Cathy: apples
+Bob: bananas
+```
+

pkg/yqlib/doc/Split into Documents.md

@@ -0,0 +1,31 @@
+# Split into Documents
+
+This operator splits all matches into separate documents
+
+## Split empty
+Running
+```bash
+yq eval --null-input 'splitDoc'
+```
+will output
+```yaml
+
+```
+
+## Split array
+Given a sample.yml file of:
+```yaml
+- a: cat
+- b: dog
+```
+then
+```bash
+yq eval '.[] | splitDoc' sample.yml
+```
+will output
+```yaml
+a: cat
+---
+b: dog
+```
+

pkg/yqlib/doc/String Operators.md

@@ -0,0 +1,88 @@
+# String Operators
+
+## Join strings
+Given a sample.yml file of:
+```yaml
+- cat
+- meow
+- 1
+- null
+- true
+```
+then
+```bash
+yq eval 'join("; ")' sample.yml
+```
+will output
+```yaml
+cat; meow; 1; ; true
+```
+
+## Substitute / Replace string
+This uses golang regex, described [here](https://github.com/google/re2/wiki/Syntax)
+Note the use of `|=` to run in context of the current string value.
+
+Given a sample.yml file of:
+```yaml
+a: dogs are great
+```
+then
+```bash
+yq eval '.a |= sub("dogs", "cats")' sample.yml
+```
+will output
+```yaml
+a: cats are great
+```
+
+## Substitute / Replace string with regex
+This uses golang regex, described [here](https://github.com/google/re2/wiki/Syntax)
+Note the use of `|=` to run in context of the current string value.
+
+Given a sample.yml file of:
+```yaml
+a: cat
+b: heat
+```
+then
+```bash
+yq eval '.[] |= sub("(a)", "${1}r")' sample.yml
+```
+will output
+```yaml
+a: cart
+b: heart
+```
+
+## Split strings
+Given a sample.yml file of:
+```yaml
+cat; meow; 1; ; true
+```
+then
+```bash
+yq eval 'split("; ")' sample.yml
+```
+will output
+```yaml
+- cat
+- meow
+- "1"
+- ""
+- "true"
+```
+
+## Split strings one match
+Given a sample.yml file of:
+```yaml
+word
+```
+then
+```bash
+yq eval 'split("; ")' sample.yml
+```
+will output
+```yaml
+- word
+```
+

pkg/yqlib/doc/Style.md

@@ -1,4 +1,42 @@
 The style operator can be used to get or set the style of nodes (e.g. string style, yaml style)
+## Update and set style of a particular node (simple)
+Given a sample.yml file of:
+```yaml
+a:
+  b: thing
+  c: something
+```
+then
+```bash
+yq eval '.a.b = "new" | .a.b style="double"' sample.yml
+```
+will output
+```yaml
+a:
+  b: "new"
+  c: something
+```
+
+## Update and set style of a particular node using path variables
+You can use a variable to re-use a path
+
+Given a sample.yml file of:
+```yaml
+a:
+  b: thing
+  c: something
+```
+then
+```bash
+yq eval '.a.b as $x | $x = "new" | $x style="double"' sample.yml
+```
+will output
+```yaml
+a:
+  b: "new"
+  c: something
+```
+
 ## Set tagged style
 Given a sample.yml file of:
 ```yaml
@@ -40,6 +78,26 @@ c: "3.2"
 e: "true"
 ```
 
+## Set double quote style on map keys too
+Given a sample.yml file of:
+```yaml
+a: cat
+b: 5
+c: 3.2
+e: true
+```
+then
+```bash
+yq eval '... style="double"' sample.yml
+```
+will output
+```yaml
+"a": "cat"
+"b": "5"
+"c": "3.2"
+"e": "true"
+```
+
 ## Set single quote style
 Given a sample.yml file of:
 ```yaml
@@ -125,19 +183,19 @@ will output
 {a: cat, b: 5, c: 3.2, e: true}
 ```
 
-## Pretty print
-Set empty (default) quote style
+## Reset style - or pretty print
+Set empty (default) quote style, note the usage of `...` to match keys too. Note that there is a `--prettyPrint/-P` short flag for this.
 
 Given a sample.yml file of:
 ```yaml
 a: cat
-b: 5
-c: 3.2
-e: true
+"b": 5
+'c': 3.2
+"e": true
 ```
 then
 ```bash
-yq eval '.. style=""' sample.yml
+yq eval '... style=""' sample.yml
 ```
 will output
 ```yaml
@@ -147,6 +205,22 @@ c: 3.2
 e: true
 ```
 
+## Set style relatively with assign-update
+Given a sample.yml file of:
+```yaml
+a: single
+b: double
+```
+then
+```bash
+yq eval '.[] style |= .' sample.yml
+```
+will output
+```yaml
+a: 'single'
+b: "double"
+```
+
 ## Read style
 Given a sample.yml file of:
 ```yaml

pkg/yqlib/doc/Subtract.md

@@ -0,0 +1,71 @@
+
+## Number subtraction - float
+If the lhs or rhs are floats then the expression will be calculated with floats.
+
+Given a sample.yml file of:
+```yaml
+a: 3
+b: 4.5
+```
+then
+```bash
+yq eval '.a = .a - .b' sample.yml
+```
+will output
+```yaml
+a: -1.5
+b: 4.5
+```
+
+## Number subtraction - float
+If the lhs or rhs are floats then the expression will be calculated with floats.
+
+Given a sample.yml file of:
+```yaml
+a: 3
+b: 4.5
+```
+then
+```bash
+yq eval '.a = .a - .b' sample.yml
+```
+will output
+```yaml
+a: -1.5
+b: 4.5
+```
+
+## Number subtraction - int
+If both the lhs and rhs are ints then the expression will be calculated with ints.
+
+Given a sample.yml file of:
+```yaml
+a: 3
+b: 4
+```
+then
+```bash
+yq eval '.a = .a - .b' sample.yml
+```
+will output
+```yaml
+a: -1
+b: 4
+```
+
+## Decrement numbers
+Given a sample.yml file of:
+```yaml
+a: 3
+b: 5
+```
+then
+```bash
+yq eval '.[] -= 1' sample.yml
+```
+will output
+```yaml
+a: 2
+b: 4
+```
+

pkg/yqlib/doc/Tag.md

@@ -22,7 +22,21 @@ will output
 !!seq
 ```
 
-## Convert numbers to strings
+## Set custom tag
+Given a sample.yml file of:
+```yaml
+a: str
+```
+then
+```bash
+yq eval '.a tag = "!!mikefarah"' sample.yml
+```
+will output
+```yaml
+a: !!mikefarah str
+```
+
+## Find numbers and convert them to strings
 Given a sample.yml file of:
 ```yaml
 a: cat

pkg/yqlib/doc/Traverse (Read).md

@@ -32,8 +32,23 @@ b: apple
 c: banana
 ```
 
+## Optional Splat
+Just like splat, but won't error if you run it against scalars
+
+Given a sample.yml file of:
+```yaml
+cat
+```
+then
+```bash
+yq eval '.[]' sample.yml
+```
+will output
+```yaml
+```
+
 ## Special characters
-Use quotes around path elements with special characters
+Use quotes with brackets around path elements with special characters
 
 Given a sample.yml file of:
 ```yaml
@@ -41,13 +56,47 @@ Given a sample.yml file of:
 ```
 then
 ```bash
-yq eval '."{}"' sample.yml
+yq eval '.["{}"]' sample.yml
 ```
 will output
 ```yaml
 frog
 ```
 
+## Keys with spaces
+Use quotes with brackets around path elements with special characters
+
+Given a sample.yml file of:
+```yaml
+"red rabbit": frog
+```
+then
+```bash
+yq eval '.["red rabbit"]' sample.yml
+```
+will output
+```yaml
+frog
+```
+
+## Dynamic keys
+Expressions within [] can be used to dynamically lookup / calculate keys
+
+Given a sample.yml file of:
+```yaml
+b: apple
+apple: crispy yum
+banana: soft yum
+```
+then
+```bash
+yq eval '.[.b]' sample.yml
+```
+will output
+```yaml
+crispy yum
+```
+
 ## Children don't exist
 Nodes are added dynamically while traversing
 
@@ -64,6 +113,23 @@ will output
 null
 ```
 
+## Optional identifier
+Like jq, does not output an error when the yaml is not an array or object as expected
+
+Given a sample.yml file of:
+```yaml
+- 1
+- 2
+- 3
+```
+then
+```bash
+yq eval '.a?' sample.yml
+```
+will output
+```yaml
+```
+
 ## Wildcard matching
 Given a sample.yml file of:
 ```yaml
@@ -106,7 +172,7 @@ b: *cat
 ```
 then
 ```bash
-yq eval '.b.[]' sample.yml
+yq eval '.b[]' sample.yml
 ```
 will output
 ```yaml
@@ -290,7 +356,7 @@ foobar:
 ```
 then
 ```bash
-yq eval '.foobar.[]' sample.yml
+yq eval '.foobar[]' sample.yml
 ```
 will output
 ```yaml
@@ -356,7 +422,7 @@ foobar:
 ```
 then
 ```bash
-yq eval '.foobarList.[]' sample.yml
+yq eval '.foobarList[]' sample.yml
 ```
 will output
 ```yaml
@@ -366,3 +432,21 @@ bar_thing
 foobarList_c
 ```
 
+## Select multiple indices
+Given a sample.yml file of:
+```yaml
+a:
+  - a
+  - b
+  - c
+```
+then
+```bash
+yq eval '.a[0, 2]' sample.yml
+```
+will output
+```yaml
+a
+c
+```
+

pkg/yqlib/doc/Unique.md

@@ -0,0 +1,82 @@
+This is used to filter out duplicated items in an array.
+
+## Unique array of scalars (string/numbers)
+Given a sample.yml file of:
+```yaml
+- 1
+- 2
+- 3
+- 2
+```
+then
+```bash
+yq eval 'unique' sample.yml
+```
+will output
+```yaml
+- 1
+- 2
+- 3
+```
+
+## Unique nulls
+Unique works on the node value, so it considers different representations of nulls to be different
+
+Given a sample.yml file of:
+```yaml
+- ~
+- null
+- ~
+- null
+```
+then
+```bash
+yq eval 'unique' sample.yml
+```
+will output
+```yaml
+- ~
+- null
+```
+
+## Unique all nulls
+Run against the node tag to unique all the nulls
+
+Given a sample.yml file of:
+```yaml
+- ~
+- null
+- ~
+- null
+```
+then
+```bash
+yq eval 'unique_by(tag)' sample.yml
+```
+will output
+```yaml
+- ~
+```
+
+## Unique array object fields
+Given a sample.yml file of:
+```yaml
+- name: harry
+  pet: cat
+- name: billy
+  pet: dog
+- name: harry
+  pet: dog
+```
+then
+```bash
+yq eval 'unique_by(.name)' sample.yml
+```
+will output
+```yaml
+- name: harry
+  pet: cat
+- name: billy
+  pet: dog
+```
+

pkg/yqlib/doc/Variable Operators.md

@@ -0,0 +1,58 @@
+For more complex scenarios, variables can be used to hold values of expression to be used in other expressions.
+
+## Single value variable
+Given a sample.yml file of:
+```yaml
+a: cat
+```
+then
+```bash
+yq eval '.a as $foo | $foo' sample.yml
+```
+will output
+```yaml
+cat
+```
+
+## Multi value variable
+Given a sample.yml file of:
+```yaml
+- cat
+- dog
+```
+then
+```bash
+yq eval '.[] as $foo | $foo' sample.yml
+```
+will output
+```yaml
+cat
+dog
+```
+
+## Using variables as a lookup
+Example taken from [jq](https://stedolan.github.io/jq/manual/#Variable/SymbolicBindingOperator:...as$identifier|...)
+
+Given a sample.yml file of:
+```yaml
+"posts":
+  - "title": Frist psot
+    "author": anon
+  - "title": A well-written article
+    "author": person1
+"realnames":
+  "anon": Anonymous Coward
+  "person1": Person McPherson
+```
+then
+```bash
+yq eval '.realnames as $names | .posts[] | {"title":.title, "author": $names[.author]}' sample.yml
+```
+will output
+```yaml
+title: Frist psot
+author: Anonymous Coward
+title: A well-written article
+author: Person McPherson
+```
+

pkg/yqlib/doc/aa.md

@@ -0,0 +1,116 @@
+# Operators
+
+In `yq` expressions are made up of operators and pipes. A context of nodes is passed through the expression and each operation takes the context as input and returns a new context as output. That output is piped in as input for the next operation in the expression. To begin with, the context is set to the first yaml document of the first yaml file (if processing in sequence using eval).
+
+Lets look at a couple of examples.
+
+## Example with a simple operator
+
+Given a document like:
+
+```yaml
+- [a]
+- "cat"
+```
+
+with an expression:
+
+```
+.[] | length
+```
+
+`yq` will initially set the context as single node of the entire yaml document, an array of two elements.
+
+```yaml
+- [a]
+- "cat"
+```
+
+This gets piped into the splat operator `.[]` which will split out the context into a collection of two nodes `[a]` and `"cat"`. Note that this is _not_ a yaml array.
+
+The `length` operator take no arguments, and will simply return the length of _each_ matching node in the context. So for the context of `[a]` and `"cat"`, it will return a new context of `1` and `3`.
+
+This being the last operation in the expression, the results will be printed out:
+
+```
+1
+3
+```
+
+# Example with an operator that takes arguments.
+
+Given a document like:
+
+```yaml
+a: cat
+b: dog
+```
+
+with an expression:
+
+```
+.a = .b
+```
+
+The `=` operator takes two arguments, a `lhs` expression, which in this case is `.a` and `rhs` expression which is `.b`. 
+
+It pipes the current, lets call it 'root' context through the `lhs` expression of `.a` to return the node 
+
+```yaml
+cat
+```
+
+Note that this node holds not only its value 'cat', but comments and metadata too, including path and parent information.
+
+The `=` operator then pipes the 'root' context through the `rhs` expression of `.b` to return the node
+
+```yaml
+dog
+```
+
+Both sides have now been evaluated, so now the operator copies across the value from the RHS to the value on the LHS, and it returns the now updated context:
+
+```yaml
+a: dog
+b: dog
+```
+
+# Relative update (e.g. `|=`)
+There is another form of the `=` operator which we call the relative form. It's very similar to `=` but with one key difference when evaluating the RHS expression.
+
+In the plain form, we pass in the 'root' level context to the RHS expression. In relative form, we pass in _each result of the LHS_ to the RHS expression. Let's go through an example.
+
+Given a document like:
+
+```yaml
+a: 1
+b: thing
+```
+
+with an expression:
+
+```
+.a |= . + 1
+```
+
+Similar to the `=` operator, `|=` takes two operands, the LHS and RHS.
+
+It pipes the current context (the whole document) through the LHS expression  of `.a` to get the node value:
+
+```
+1
+```
+
+Now it pipes _that LHS context_ into the RHS expression `. + 1` (whereas in the `=` plain form it piped the original document context into the RHS) to yield:
+
+
+```
+2
+```
+
+The assignment operator then copies across the value from the RHS to the value on the LHS, and it returns the now updated 'root' context:
+
+```yaml
+a: 2
+b: thing
+```

pkg/yqlib/doc/headers/Add.md

@@ -1,6 +1,6 @@
 Add behaves differently according to the type of the LHS:
 - arrays: concatenate
-- number scalars: arithmetic addition (soon)
-- string scalars: concatenate (soon)
+- number scalars: arithmetic addition
+- string scalars: concatenate
 
-Use `+=` as append assign for things like increment. `.a += .x` is equivalent to running `.a |= . + .x`.
+Use `+=` as append assign for things like increment. Note that `.a += .x` is equivalent to running `.a = .a + .x`.

pkg/yqlib/doc/headers/Alternative (Default value).md

@@ -0,0 +1 @@
+This operator is used to provide alternative (or default) values when a particular expression is either null or false.

pkg/yqlib/doc/headers/Anchor and Alias Operators.md

@@ -0,0 +1,4 @@
+Use the `alias` and `anchor` operators to read and write yaml aliases and anchors. The `explode` operator normalises a yaml file (dereference (or expands) aliases and remove anchor names).
+
+`yq` supports merge aliases (like `<<: *blah`) however this is no longer in the standard yaml spec (1.2) and so `yq` will automatically add the `!!merge` tag to these nodes as it is effectively a custom tag.
+

pkg/yqlib/doc/headers/Boolean Operators.md

@@ -1 +1,9 @@
-The `or` and `and` operators take two parameters and return a boolean result. `not` flips a boolean from true to false, or vice versa. These are most commonly used with the `select` operator to filter particular nodes.
+The `or` and `and` operators take two parameters and return a boolean result. 
+
+`not` flips a boolean from true to false, or vice versa. 
+
+`any` will return `true` if there are any `true` values in a array sequence, and `all` will return true if _all_ elements in an array are true.
+
+`any_c(condition)` and `all_c(condition)` are like `any` and `all` but they take a condition expression that is used against each element to determine if it's `true`. Note: in `jq` you can simply pass a condition to `any` or `all` and it simply works - `yq` isn't that clever..yet
+
+These are most commonly used with the `select` operator to filter particular nodes.

pkg/yqlib/doc/headers/Comment Operators.md

@@ -1 +1,11 @@
-Use these comment operators to set or retrieve comments.
+Use these comment operators to set or retrieve comments.
+
+Like the `=` and `|=` assign operators, the same syntax applies when updating comments:
+
+
+### plain form: `=`
+This will assign the LHS nodes comments to the expression on the RHS. The RHS is run against the matching nodes in the pipeline
+
+### relative form: `|=` 
+Similar to the plain form, however the RHS evaluates against each matching LHS node! This is useful if you want to set the comments as a relative expression of the node, for instance its value or path.
+

pkg/yqlib/doc/headers/Document Index.md

@@ -1 +1 @@
-Use the `documentIndex` operator to select nodes of a particular document.
+Use the `documentIndex` operator (or the `di` shorthand) to select nodes of a particular document.

pkg/yqlib/doc/headers/Entries.md

@@ -0,0 +1 @@
+Similar to the same named functions in `jq` these functions convert to/from an object and an array of key-value pairs. This is most useful for performing operations on keys of maps.

pkg/yqlib/doc/headers/Env Variable Operators.md

@@ -0,0 +1,2 @@
+This operator is used to handle environment variables usage in path expressions. While environment variables can, of course, be passed in via your CLI with string interpolation, this often comes with complex quote escaping and can be tricky to write and read. Note that there are two forms, `env` which will parse the environment variable as a yaml (be it a map, array, string, number of boolean) and `strenv` which will always parse the argument as a string.
+

pkg/yqlib/doc/headers/Explode.md

@@ -1 +0,0 @@
-Explodes (or dereferences) aliases and anchors.

pkg/yqlib/doc/headers/File Operators.md

@@ -1,7 +1,9 @@
 File operators are most often used with merge when needing to merge specific files together. Note that when doing this, you will need to use `eval-all` to ensure all yaml documents are loaded into memory before performing the merge (as opposed to `eval` which runs the expression once per document).
 
+Note that the `fileIndex` operator has a short alias of `fi`.
+
 ## Merging files
 Note the use of eval-all to ensure all documents are loaded into memory.
 ```bash
-yq eval-all 'select(fileIndex == 0) * select(filename == "file2.yaml")' file1.yaml file2.yaml
+yq eval-all 'select(fi == 0) * select(filename == "file2.yaml")' file1.yaml file2.yaml
 ```

pkg/yqlib/doc/headers/Keys.md

@@ -0,0 +1,3 @@
+# Keys
+
+Use the `keys` operator to return map keys or array indices. 

pkg/yqlib/doc/headers/Multiply (Merge).md

@@ -0,0 +1,20 @@
+Like the multiple operator in jq, depending on the operands, this multiply operator will do different things. Currently numbers, arrays and objects are supported.
+
+## Objects and arrays - merging
+Objects are merged deeply matching on matching keys. By default, array values override and are not deeply merged.
+
+Note that when merging objects, this operator returns the merged object (not the parent). This will be clearer in the examples below.
+
+### Merge Flags
+You can control how objects are merged by using one or more of the following flags. Multiple flags can be used together, e.g. `.a *+? .b`.  See examples below
+
+- `+` to append arrays
+- `?` to only merge existing fields
+- `d` to deeply merge arrays
+
+### Merging files
+Note the use of `eval-all` to ensure all documents are loaded into memory.
+
+```bash
+yq eval-all 'select(fileIndex == 0) * select(fileIndex == 1)' file1.yaml file2.yaml
+```

pkg/yqlib/doc/headers/Multiply.md

@@ -1,14 +0,0 @@
-Like the multiple operator in `jq`, depending on the operands, this multiply operator will do different things. Currently only objects are supported, which have the effect of merging the RHS into the LHS.
-
-Upcoming versions of `yq` will add support for other types of multiplication (numbers, strings).
-
-To concatenate when merging objects, use the `*+` form (see examples below). This will recursively merge objects, appending arrays when it encounters them.
-
-Note that when merging objects, this operator returns the merged object (not the parent). This will be clearer in the examples below.
-
-## Merging files
-Note the use of eval-all to ensure all documents are loaded into memory.
-
-```bash
-yq eval-all 'select(fileIndex == 0) * select(fileIndex == 1)' file1.yaml file2.yaml
-```

pkg/yqlib/doc/headers/Recursive Descent (Glob).md

@@ -0,0 +1,19 @@
+This operator recursively matches (or globs) all children nodes given of a particular element, including that node itself. This is most often used to apply a filter recursively against all matches. It can be used in either the 
+
+## match values form `..`
+This will, like the `jq` equivalent, recursively match all _value_ nodes. Use it to find/manipulate particular values.
+
+For instance to set the `style` of all _value_ nodes in a yaml doc, excluding map keys:
+
+```bash
+yq eval '.. style= "flow"' file.yaml
+```
+
+## match values and map keys form `...`
+The also includes map keys in the results set. This is particularly useful in YAML as unlike JSON, map keys can have their own styling, tags and use anchors and aliases.
+
+For instance to set the `style` of all nodes in a yaml doc, including the map keys:
+
+```bash
+yq eval '... style= "flow"' file.yaml
+```

pkg/yqlib/doc/headers/Recursive Descent.md

@@ -1,5 +0,0 @@
-This operator recursively matches all children nodes given of a particular element, including that node itself. This is most often used to apply a filter recursively against all matches, for instance to set the `style` of all nodes in a yaml doc:
-
-```bash
-yq eval '.. style= "flow"' file.yaml
-```

pkg/yqlib/doc/headers/Reduce.md

@@ -0,0 +1,21 @@
+Reduce is a powerful way to process a collection of data into a new form.
+
+```
+<exp> as $<name> ireduce (<init>; <block>)
+```
+
+e.g.
+
+```
+.[] as $item ireduce (0; . + $item)
+```
+
+On the LHS we are configuring the collection of items that will be reduced `<exp>` as well as what each element will be called `$<name>`. Note that the array has been splatted into its individual elements.
+
+On the RHS there is `<init>`, the starting value of the accumulator and `<block>`, the expression that will update the accumulator for each element in the collection. Note that within the block expression, `.` will evaluate to the current value of the accumulator. 
+
+## yq vs jq syntax
+Reduce syntax in `yq` is a little different from `jq` - as `yq` (currently) isn't as sophisticated as `jq` and its only supports infix notation (e.g. a + b, where the operator is in the middle of the two parameters) - where as `jq` uses a mix of infix notation with _prefix_ notation (e.g. `reduce a b` is like writing `+ a b`).
+
+To that end, the reduce operator is called `ireduce` for backwards compatability if a `jq` like prefix version of `reduce` is ever added.
+

pkg/yqlib/doc/headers/Split into Documents.md

@@ -0,0 +1,3 @@
+# Split into Documents
+
+This operator splits all matches into separate documents

pkg/yqlib/doc/headers/String Operators.md

@@ -0,0 +1 @@
+# String Operators

pkg/yqlib/doc/headers/Unique.md

@@ -0,0 +1 @@
+This is used to filter out duplicated items in an array.

pkg/yqlib/doc/headers/Variable Operators.md

@@ -0,0 +1 @@
+For more complex scenarios, variables can be used to hold values of expression to be used in other expressions.

pkg/yqlib/encoder.go

@@ -50,7 +50,7 @@ func (ye *yamlEncoder) Encode(node *yaml.Node) error {
 	}
 
 	if ye.colorise {
-		return ColorizeAndPrint(tempBuffer.Bytes(), ye.destination)
+		return colorizeAndPrint(tempBuffer.Bytes(), ye.destination)
 	}
 	return nil
 }
@@ -76,6 +76,8 @@ func mapKeysToStrings(node *yaml.Node) {
 
 func NewJsonEncoder(destination io.Writer, indent int) Encoder {
 	var encoder = json.NewEncoder(destination)
+	encoder.SetEscapeHTML(false) // do not escape html chars e.g. &, <, >
+
 	var indentString = ""
 
 	for index := 0; index < indent; index++ {
@@ -153,11 +155,15 @@ func (o *orderedMap) UnmarshalJSON(data []byte) error {
 }
 
 func (o orderedMap) MarshalJSON() ([]byte, error) {
-	if o.kv == nil {
-		return json.Marshal(o.altVal)
-	}
 	buf := new(bytes.Buffer)
 	enc := json.NewEncoder(buf)
+	enc.SetEscapeHTML(false) // do not escape html chars e.g. &, <, >
+	if o.kv == nil {
+		if err := enc.Encode(o.altVal); err != nil {
+			return nil, err
+		}
+		return buf.Bytes(), nil
+	}
 	buf.WriteByte('{')
 	for idx, el := range o.kv {
 		if err := enc.Encode(el.K); err != nil {

pkg/yqlib/encoder_test.go

@@ -9,29 +9,11 @@ import (
 	"github.com/mikefarah/yq/v4/test"
 )
 
-var sampleYaml = `zabbix: winner
-apple: great
-banana:
-- {cobra: kai, angus: bob}
-`
-
-var expectedJson = `{
-  "zabbix": "winner",
-  "apple": "great",
-  "banana": [
-    {
-      "cobra": "kai",
-      "angus": "bob"
-    }
-  ]
-}
-`
-
-func TestJsonEncoderPreservesObjectOrder(t *testing.T) {
+func yamlToJson(sampleYaml string, indent int) string {
 	var output bytes.Buffer
 	writer := bufio.NewWriter(&output)
 
-	var jsonEncoder = NewJsonEncoder(writer, 2)
+	var jsonEncoder = NewJsonEncoder(writer, indent)
 	inputs, err := readDocuments(strings.NewReader(sampleYaml), "sample.yml", 0)
 	if err != nil {
 		panic(err)
@@ -42,6 +24,33 @@ func TestJsonEncoderPreservesObjectOrder(t *testing.T) {
 		panic(err)
 	}
 	writer.Flush()
-	test.AssertResult(t, expectedJson, output.String())
 
+	return strings.TrimSuffix(output.String(), "\n")
+}
+
+func TestJsonEncoderPreservesObjectOrder(t *testing.T) {
+	var sampleYaml = `zabbix: winner
+apple: great
+banana:
+- {cobra: kai, angus: bob}
+`
+	var expectedJson = `{
+  "zabbix": "winner",
+  "apple": "great",
+  "banana": [
+    {
+      "cobra": "kai",
+      "angus": "bob"
+    }
+  ]
+}`
+	var actualJson = yamlToJson(sampleYaml, 2)
+	test.AssertResult(t, expectedJson, actualJson)
+}
+
+func TestJsonEncoderDoesNotEscapeHTMLChars(t *testing.T) {
+	var sampleYaml = `build: "( ./lint && ./format && ./compile ) < src.code"`
+	var expectedJson = `{"build":"( ./lint && ./format && ./compile ) < src.code"}`
+	var actualJson = yamlToJson(sampleYaml, 0)
+	test.AssertResult(t, expectedJson, actualJson)
 }

pkg/yqlib/expression_parser.go

@@ -0,0 +1,75 @@
+package yqlib
+
+import (
+	"fmt"
+	"strings"
+)
+
+type ExpressionNode struct {
+	Operation *Operation
+	Lhs       *ExpressionNode
+	Rhs       *ExpressionNode
+}
+
+type ExpressionParser interface {
+	ParseExpression(expression string) (*ExpressionNode, error)
+}
+
+type expressionParserImpl struct {
+	pathTokeniser expressionTokeniser
+	pathPostFixer expressionPostFixer
+}
+
+func NewExpressionParser() ExpressionParser {
+	return &expressionParserImpl{newExpressionTokeniser(), newExpressionPostFixer()}
+}
+
+func (p *expressionParserImpl) ParseExpression(expression string) (*ExpressionNode, error) {
+	tokens, err := p.pathTokeniser.Tokenise(expression)
+	if err != nil {
+		return nil, err
+	}
+	var Operations []*Operation
+	Operations, err = p.pathPostFixer.ConvertToPostfix(tokens)
+	if err != nil {
+		return nil, err
+	}
+	return p.createExpressionTree(Operations)
+}
+
+func (p *expressionParserImpl) createExpressionTree(postFixPath []*Operation) (*ExpressionNode, error) {
+	var stack = make([]*ExpressionNode, 0)
+
+	if len(postFixPath) == 0 {
+		return nil, nil
+	}
+
+	for _, Operation := range postFixPath {
+		var newNode = ExpressionNode{Operation: Operation}
+		log.Debugf("pathTree %v ", Operation.toString())
+		if Operation.OperationType.NumArgs > 0 {
+			numArgs := Operation.OperationType.NumArgs
+			if numArgs == 1 {
+				if len(stack) < 1 {
+					return nil, fmt.Errorf("'%v' expects 1 arg but received none", strings.TrimSpace(Operation.StringValue))
+				}
+				remaining, rhs := stack[:len(stack)-1], stack[len(stack)-1]
+				newNode.Rhs = rhs
+				stack = remaining
+			} else if numArgs == 2 {
+				if len(stack) < 2 {
+					return nil, fmt.Errorf("'%v' expects 2 args but there is %v", strings.TrimSpace(Operation.StringValue), len(stack))
+				}
+				remaining, lhs, rhs := stack[:len(stack)-2], stack[len(stack)-2], stack[len(stack)-1]
+				newNode.Lhs = lhs
+				newNode.Rhs = rhs
+				stack = remaining
+			}
+		}
+		stack = append(stack, &newNode)
+	}
+	if len(stack) != 1 {
+		return nil, fmt.Errorf("Bad expression, please check expression syntax")
+	}
+	return stack[0], nil
+}

pkg/yqlib/expression_parser_test.go

@@ -0,0 +1,42 @@
+package yqlib
+
+import (
+	"testing"
+
+	"github.com/mikefarah/yq/v4/test"
+)
+
+func TestPathTreeNoArgsForTwoArgOp(t *testing.T) {
+	_, err := NewExpressionParser().ParseExpression("=")
+	test.AssertResultComplex(t, "'=' expects 2 args but there is 0", err.Error())
+}
+
+func TestPathTreeOneLhsArgsForTwoArgOp(t *testing.T) {
+	_, err := NewExpressionParser().ParseExpression(".a =")
+	test.AssertResultComplex(t, "'=' expects 2 args but there is 1", err.Error())
+}
+
+func TestPathTreeOneRhsArgsForTwoArgOp(t *testing.T) {
+	_, err := NewExpressionParser().ParseExpression("= .a")
+	test.AssertResultComplex(t, "'=' expects 2 args but there is 1", err.Error())
+}
+
+func TestPathTreeTwoArgsForTwoArgOp(t *testing.T) {
+	_, err := NewExpressionParser().ParseExpression(".a = .b")
+	test.AssertResultComplex(t, nil, err)
+}
+
+func TestPathTreeNoArgsForOneArgOp(t *testing.T) {
+	_, err := NewExpressionParser().ParseExpression("explode")
+	test.AssertResultComplex(t, "'explode' expects 1 arg but received none", err.Error())
+}
+
+func TestPathTreeOneArgForOneArgOp(t *testing.T) {
+	_, err := NewExpressionParser().ParseExpression("explode(.)")
+	test.AssertResultComplex(t, nil, err)
+}
+
+func TestPathTreeExtraArgs(t *testing.T) {
+	_, err := NewExpressionParser().ParseExpression("sortKeys(.) explode(.)")
+	test.AssertResultComplex(t, "Bad expression, please check expression syntax", err.Error())
+}

pkg/yqlib/expression_postfix.go

@@ -0,0 +1,109 @@
+package yqlib
+
+import (
+	"errors"
+
+	logging "gopkg.in/op/go-logging.v1"
+)
+
+type expressionPostFixer interface {
+	ConvertToPostfix([]*token) ([]*Operation, error)
+}
+
+type expressionPostFixerImpl struct {
+}
+
+func newExpressionPostFixer() expressionPostFixer {
+	return &expressionPostFixerImpl{}
+}
+
+func popOpToResult(opStack []*token, result []*Operation) ([]*token, []*Operation) {
+	var newOp *token
+	opStack, newOp = opStack[0:len(opStack)-1], opStack[len(opStack)-1]
+	log.Debugf("popped %v from opstack to results", newOp.toString(true))
+	return opStack, append(result, newOp.Operation)
+}
+
+func (p *expressionPostFixerImpl) ConvertToPostfix(infixTokens []*token) ([]*Operation, error) {
+	var result []*Operation
+	// surround the whole thing with brackets
+	var opStack = []*token{{TokenType: openBracket}}
+	var tokens = append(infixTokens, &token{TokenType: closeBracket})
+
+	for _, currentToken := range tokens {
+		log.Debugf("postfix processing currentToken %v", currentToken.toString(true))
+		switch currentToken.TokenType {
+		case openBracket, openCollect, openCollectObject:
+			opStack = append(opStack, currentToken)
+			log.Debugf("put %v onto the opstack", currentToken.toString(true))
+		case closeCollect, closeCollectObject:
+			var opener tokenType = openCollect
+			var collectOperator *operationType = collectOpType
+			if currentToken.TokenType == closeCollectObject {
+				opener = openCollectObject
+				collectOperator = collectObjectOpType
+			}
+
+			for len(opStack) > 0 && opStack[len(opStack)-1].TokenType != opener {
+				opStack, result = popOpToResult(opStack, result)
+			}
+			if len(opStack) == 0 {
+				return nil, errors.New("Bad path expression, got close collect brackets without matching opening bracket")
+			}
+			// now we should have [ as the last element on the opStack, get rid of it
+			opStack = opStack[0 : len(opStack)-1]
+			log.Debugf("deleteing open bracket from opstack")
+
+			//and append a collect to the result
+			// hack - see if there's the optional traverse flag
+			// on the close op - move it to the collect op.
+			// allows for .["cat"]?
+			prefs := traversePreferences{}
+			closeTokenMatch := string(currentToken.Match.Bytes)
+			if closeTokenMatch[len(closeTokenMatch)-1:] == "?" {
+				prefs.OptionalTraverse = true
+			}
+			result = append(result, &Operation{OperationType: collectOperator, Preferences: prefs})
+			log.Debugf("put collect onto the result")
+			result = append(result, &Operation{OperationType: shortPipeOpType})
+			log.Debugf("put shortpipe onto the result")
+
+			//traverseArrayCollect is a sneaky op that needs to be included too
+			//when closing a []
+			if len(opStack) > 0 && opStack[len(opStack)-1].Operation != nil && opStack[len(opStack)-1].Operation.OperationType == traverseArrayOpType {
+				opStack, result = popOpToResult(opStack, result)
+			}
+
+		case closeBracket:
+			for len(opStack) > 0 && opStack[len(opStack)-1].TokenType != openBracket {
+				opStack, result = popOpToResult(opStack, result)
+			}
+			if len(opStack) == 0 {
+				return nil, errors.New("Bad path expression, got close brackets without matching opening bracket")
+			}
+			// now we should have ( as the last element on the opStack, get rid of it
+			opStack = opStack[0 : len(opStack)-1]
+
+		default:
+			var currentPrecedence = currentToken.Operation.OperationType.Precedence
+			// pop off higher precedent operators onto the result
+			for len(opStack) > 0 &&
+				opStack[len(opStack)-1].TokenType == operationToken &&
+				opStack[len(opStack)-1].Operation.OperationType.Precedence > currentPrecedence {
+				opStack, result = popOpToResult(opStack, result)
+			}
+			// add this operator to the opStack
+			opStack = append(opStack, currentToken)
+			log.Debugf("put %v onto the opstack", currentToken.toString(true))
+		}
+	}
+
+	if log.IsEnabledFor(logging.DEBUG) {
+		log.Debugf("PostFix Result:")
+		for _, currentToken := range result {
+			log.Debugf("> %v", currentToken.toString())
+		}
+	}
+
+	return result, nil
+}

pkg/yqlib/expression_processing_test.go

@@ -0,0 +1,276 @@
+package yqlib
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/mikefarah/yq/v4/test"
+)
+
+var pathTests = []struct {
+	path            string
+	expectedTokens  []interface{}
+	expectedPostFix []interface{}
+}{
+	{
+		`.[0]`,
+		append(make([]interface{}, 0), "SELF", "TRAVERSE_ARRAY", "[", "0 (int64)", "]"),
+		append(make([]interface{}, 0), "SELF", "0 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
+	{
+		`.[0][1]`,
+		append(make([]interface{}, 0), "SELF", "TRAVERSE_ARRAY", "[", "0 (int64)", "]", "TRAVERSE_ARRAY", "[", "1 (int64)", "]"),
+		append(make([]interface{}, 0), "SELF", "0 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "1 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
+	{
+		`"\""`,
+		append(make([]interface{}, 0), "\" (string)"),
+		append(make([]interface{}, 0), "\" (string)"),
+	},
+	{
+		`[]|join(".")`,
+		append(make([]interface{}, 0), "[", "EMPTY", "]", "PIPE", "JOIN", "(", ". (string)", ")"),
+		append(make([]interface{}, 0), "EMPTY", "COLLECT", "SHORT_PIPE", ". (string)", "JOIN", "PIPE"),
+	},
+	{
+		`{"cool": .b or .c}`,
+		append(make([]interface{}, 0), "{", "cool (string)", "CREATE_MAP", "b", "OR", "c", "}"),
+		append(make([]interface{}, 0), "cool (string)", "b", "c", "OR", "CREATE_MAP", "COLLECT_OBJECT", "SHORT_PIPE"),
+	},
+	{
+		`{"cool": []|join(".")}`,
+		append(make([]interface{}, 0), "{", "cool (string)", "CREATE_MAP", "[", "EMPTY", "]", "PIPE", "JOIN", "(", ". (string)", ")", "}"),
+		append(make([]interface{}, 0), "cool (string)", "EMPTY", "COLLECT", "SHORT_PIPE", ". (string)", "JOIN", "PIPE", "CREATE_MAP", "COLLECT_OBJECT", "SHORT_PIPE"),
+	},
+	{
+		`.a as $item ireduce (0; . + $item)`, // note - add code to shuffle reduce to this position for postfix
+		append(make([]interface{}, 0), "a", "ASSIGN_VARIABLE", "GET_VARIABLE", "REDUCE", "(", "0 (int64)", "BLOCK", "SELF", "ADD", "GET_VARIABLE", ")"),
+		append(make([]interface{}, 0), "a", "GET_VARIABLE", "ASSIGN_VARIABLE", "0 (int64)", "SELF", "GET_VARIABLE", "ADD", "BLOCK", "REDUCE"),
+	},
+	{
+		`.a | .b | .c`,
+		append(make([]interface{}, 0), "a", "PIPE", "b", "PIPE", "c"),
+		append(make([]interface{}, 0), "a", "b", "c", "PIPE", "PIPE"),
+	},
+	{
+		`[]`,
+		append(make([]interface{}, 0), "[", "EMPTY", "]"),
+		append(make([]interface{}, 0), "EMPTY", "COLLECT", "SHORT_PIPE"),
+	},
+	{
+		`{}`,
+		append(make([]interface{}, 0), "{", "EMPTY", "}"),
+		append(make([]interface{}, 0), "EMPTY", "COLLECT_OBJECT", "SHORT_PIPE"),
+	},
+	{
+		`[{}]`,
+		append(make([]interface{}, 0), "[", "{", "EMPTY", "}", "]"),
+		append(make([]interface{}, 0), "EMPTY", "COLLECT_OBJECT", "SHORT_PIPE", "COLLECT", "SHORT_PIPE"),
+	},
+	{
+		`.realnames as $names | $names["anon"]`,
+		append(make([]interface{}, 0), "realnames", "ASSIGN_VARIABLE", "GET_VARIABLE", "PIPE", "GET_VARIABLE", "TRAVERSE_ARRAY", "[", "anon (string)", "]"),
+		append(make([]interface{}, 0), "realnames", "GET_VARIABLE", "ASSIGN_VARIABLE", "GET_VARIABLE", "anon (string)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "PIPE"),
+	},
+	{
+		`.b[.a]`,
+		append(make([]interface{}, 0), "b", "TRAVERSE_ARRAY", "[", "a", "]"),
+		append(make([]interface{}, 0), "b", "a", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
+	{
+		`.b[.a]?`,
+		append(make([]interface{}, 0), "b", "TRAVERSE_ARRAY", "[", "a", "]"),
+		append(make([]interface{}, 0), "b", "a", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
+	{
+		`.[]`,
+		append(make([]interface{}, 0), "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]"),
+		append(make([]interface{}, 0), "SELF", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
+	{
+		`.a[]`,
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "EMPTY", "]"),
+		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
+	{
+		`.a[]?`,
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "EMPTY", "]"),
+		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
+	{
+		`.a.[]`,
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "EMPTY", "]"),
+		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
+	{
+		`.a[0]`,
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "0 (int64)", "]"),
+		append(make([]interface{}, 0), "a", "0 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
+	{
+		`.a[0]?`,
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "0 (int64)", "]"),
+		append(make([]interface{}, 0), "a", "0 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
+	{
+		`.a.[0]`,
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "0 (int64)", "]"),
+		append(make([]interface{}, 0), "a", "0 (int64)", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY"),
+	},
+	{
+		`.a[].c`,
+		append(make([]interface{}, 0), "a", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "SHORT_PIPE", "c"),
+		append(make([]interface{}, 0), "a", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "c", "SHORT_PIPE"),
+	},
+	{
+		`[3]`,
+		append(make([]interface{}, 0), "[", "3 (int64)", "]"),
+		append(make([]interface{}, 0), "3 (int64)", "COLLECT", "SHORT_PIPE"),
+	},
+	{
+		`.key.array + .key.array2`,
+		append(make([]interface{}, 0), "key", "SHORT_PIPE", "array", "ADD", "key", "SHORT_PIPE", "array2"),
+		append(make([]interface{}, 0), "key", "array", "SHORT_PIPE", "key", "array2", "SHORT_PIPE", "ADD"),
+	},
+	{
+		`.key.array * .key.array2`,
+		append(make([]interface{}, 0), "key", "SHORT_PIPE", "array", "MULTIPLY", "key", "SHORT_PIPE", "array2"),
+		append(make([]interface{}, 0), "key", "array", "SHORT_PIPE", "key", "array2", "SHORT_PIPE", "MULTIPLY"),
+	},
+	{
+		`.key.array // .key.array2`,
+		append(make([]interface{}, 0), "key", "SHORT_PIPE", "array", "ALTERNATIVE", "key", "SHORT_PIPE", "array2"),
+		append(make([]interface{}, 0), "key", "array", "SHORT_PIPE", "key", "array2", "SHORT_PIPE", "ALTERNATIVE"),
+	},
+	{
+		`.a | .[].b == "apple"`,
+		append(make([]interface{}, 0), "a", "PIPE", "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "SHORT_PIPE", "b", "EQUALS", "apple (string)"),
+		append(make([]interface{}, 0), "a", "SELF", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "b", "SHORT_PIPE", "apple (string)", "EQUALS", "PIPE"),
+	},
+	{
+		`(.a | .[].b) == "apple"`,
+		append(make([]interface{}, 0), "(", "a", "PIPE", "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "SHORT_PIPE", "b", ")", "EQUALS", "apple (string)"),
+		append(make([]interface{}, 0), "a", "SELF", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "b", "SHORT_PIPE", "PIPE", "apple (string)", "EQUALS"),
+	},
+	{
+		`.[] | select(. == "*at")`,
+		append(make([]interface{}, 0), "SELF", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "PIPE", "SELECT", "(", "SELF", "EQUALS", "*at (string)", ")"),
+		append(make([]interface{}, 0), "SELF", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SELF", "*at (string)", "EQUALS", "SELECT", "PIPE"),
+	},
+	{
+		`[true]`,
+		append(make([]interface{}, 0), "[", "true (bool)", "]"),
+		append(make([]interface{}, 0), "true (bool)", "COLLECT", "SHORT_PIPE"),
+	},
+	{
+		`[true, false]`,
+		append(make([]interface{}, 0), "[", "true (bool)", "UNION", "false (bool)", "]"),
+		append(make([]interface{}, 0), "true (bool)", "false (bool)", "UNION", "COLLECT", "SHORT_PIPE"),
+	},
+	{
+		`"mike": .a`,
+		append(make([]interface{}, 0), "mike (string)", "CREATE_MAP", "a"),
+		append(make([]interface{}, 0), "mike (string)", "a", "CREATE_MAP"),
+	},
+	{
+		`.a: "mike"`,
+		append(make([]interface{}, 0), "a", "CREATE_MAP", "mike (string)"),
+		append(make([]interface{}, 0), "a", "mike (string)", "CREATE_MAP"),
+	},
+	{
+		`{"mike": .a}`,
+		append(make([]interface{}, 0), "{", "mike (string)", "CREATE_MAP", "a", "}"),
+		append(make([]interface{}, 0), "mike (string)", "a", "CREATE_MAP", "COLLECT_OBJECT", "SHORT_PIPE"),
+	},
+	{
+		`{.a: "mike"}`,
+		append(make([]interface{}, 0), "{", "a", "CREATE_MAP", "mike (string)", "}"),
+		append(make([]interface{}, 0), "a", "mike (string)", "CREATE_MAP", "COLLECT_OBJECT", "SHORT_PIPE"),
+	},
+	{
+		`{.a: .c, .b.[]: .f.g[]}`,
+		append(make([]interface{}, 0), "{", "a", "CREATE_MAP", "c", "UNION", "b", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "CREATE_MAP", "f", "SHORT_PIPE", "g", "TRAVERSE_ARRAY", "[", "EMPTY", "]", "}"),
+		append(make([]interface{}, 0), "a", "c", "CREATE_MAP", "b", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "f", "g", "EMPTY", "COLLECT", "SHORT_PIPE", "TRAVERSE_ARRAY", "SHORT_PIPE", "CREATE_MAP", "UNION", "COLLECT_OBJECT", "SHORT_PIPE"),
+	},
+	{
+		`explode(.a.b)`,
+		append(make([]interface{}, 0), "EXPLODE", "(", "a", "SHORT_PIPE", "b", ")"),
+		append(make([]interface{}, 0), "a", "b", "SHORT_PIPE", "EXPLODE"),
+	},
+	{
+		`.a.b style="folded"`,
+		append(make([]interface{}, 0), "a", "SHORT_PIPE", "b", "ASSIGN_STYLE", "folded (string)"),
+		append(make([]interface{}, 0), "a", "b", "SHORT_PIPE", "folded (string)", "ASSIGN_STYLE"),
+	},
+	{
+		`tag == "str"`,
+		append(make([]interface{}, 0), "GET_TAG", "EQUALS", "str (string)"),
+		append(make([]interface{}, 0), "GET_TAG", "str (string)", "EQUALS"),
+	},
+	{
+		`. tag= "str"`,
+		append(make([]interface{}, 0), "SELF", "ASSIGN_TAG", "str (string)"),
+		append(make([]interface{}, 0), "SELF", "str (string)", "ASSIGN_TAG"),
+	},
+	{
+		`lineComment == "str"`,
+		append(make([]interface{}, 0), "GET_COMMENT", "EQUALS", "str (string)"),
+		append(make([]interface{}, 0), "GET_COMMENT", "str (string)", "EQUALS"),
+	},
+	{
+		`. lineComment= "str"`,
+		append(make([]interface{}, 0), "SELF", "ASSIGN_COMMENT", "str (string)"),
+		append(make([]interface{}, 0), "SELF", "str (string)", "ASSIGN_COMMENT"),
+	},
+	{
+		`. lineComment |= "str"`,
+		append(make([]interface{}, 0), "SELF", "ASSIGN_COMMENT", "str (string)"),
+		append(make([]interface{}, 0), "SELF", "str (string)", "ASSIGN_COMMENT"),
+	},
+	{
+		`.a.b tag="!!str"`,
+		append(make([]interface{}, 0), "a", "SHORT_PIPE", "b", "ASSIGN_TAG", "!!str (string)"),
+		append(make([]interface{}, 0), "a", "b", "SHORT_PIPE", "!!str (string)", "ASSIGN_TAG"),
+	},
+	{
+		`""`,
+		append(make([]interface{}, 0), " (string)"),
+		append(make([]interface{}, 0), " (string)"),
+	},
+	{
+		`.foo* | (. style="flow")`,
+		append(make([]interface{}, 0), "foo*", "PIPE", "(", "SELF", "ASSIGN_STYLE", "flow (string)", ")"),
+		append(make([]interface{}, 0), "foo*", "SELF", "flow (string)", "ASSIGN_STYLE", "PIPE"),
+	},
+}
+
+var tokeniser = newExpressionTokeniser()
+var postFixer = newExpressionPostFixer()
+
+func TestPathParsing(t *testing.T) {
+	for _, tt := range pathTests {
+		tokens, err := tokeniser.Tokenise(tt.path)
+		if err != nil {
+			t.Error(tt.path, err)
+		}
+		var tokenValues []interface{}
+		for _, token := range tokens {
+			tokenValues = append(tokenValues, token.toString(false))
+		}
+		test.AssertResultComplexWithContext(t, tt.expectedTokens, tokenValues, fmt.Sprintf("tokenise: %v", tt.path))
+
+		results, errorP := postFixer.ConvertToPostfix(tokens)
+
+		var readableResults []interface{}
+		for _, token := range results {
+			readableResults = append(readableResults, token.toString())
+		}
+
+		if errorP != nil {
+			t.Error(tt.path, err)
+		}
+
+		test.AssertResultComplexWithContext(t, tt.expectedPostFix, readableResults, fmt.Sprintf("postfix: %v", tt.path))
+
+	}
+}

pkg/yqlib/expression_tokeniser.go

@@ -0,0 +1,474 @@
+package yqlib
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+
+	lex "github.com/timtadh/lexmachine"
+	"github.com/timtadh/lexmachine/machines"
+)
+
+func skip(*lex.Scanner, *machines.Match) (interface{}, error) {
+	return nil, nil
+}
+
+type tokenType uint32
+
+const (
+	operationToken = 1 << iota
+	openBracket
+	closeBracket
+	openCollect
+	closeCollect
+	openCollectObject
+	closeCollectObject
+	traverseArrayCollect
+)
+
+type token struct {
+	TokenType            tokenType
+	Operation            *Operation
+	AssignOperation      *Operation      // e.g. tag (GetTag) op becomes AssignTag if '=' follows it
+	CheckForPostTraverse bool            // e.g. [1]cat should really be [1].cat
+	Match                *machines.Match // match that created this token
+
+}
+
+func (t *token) toString(detail bool) string {
+	if t.TokenType == operationToken {
+		if detail {
+			return fmt.Sprintf("%v (%v)", t.Operation.toString(), t.Operation.OperationType.Precedence)
+		}
+		return t.Operation.toString()
+	} else if t.TokenType == openBracket {
+		return "("
+	} else if t.TokenType == closeBracket {
+		return ")"
+	} else if t.TokenType == openCollect {
+		return "["
+	} else if t.TokenType == closeCollect {
+		return "]"
+	} else if t.TokenType == openCollectObject {
+		return "{"
+	} else if t.TokenType == closeCollectObject {
+		return "}"
+	} else if t.TokenType == traverseArrayCollect {
+		return ".["
+
+	} else {
+		return "NFI"
+	}
+}
+
+func pathToken(wrapped bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		value := string(m.Bytes)
+		prefs := traversePreferences{}
+
+		if value[len(value)-1:] == "?" {
+			prefs.OptionalTraverse = true
+			value = value[:len(value)-1]
+		}
+
+		value = value[1:]
+		if wrapped {
+			value = unwrap(value)
+		}
+		log.Debug("PathToken %v", value)
+		op := &Operation{OperationType: traversePathOpType, Value: value, StringValue: value, Preferences: prefs}
+		return &token{TokenType: operationToken, Operation: op, CheckForPostTraverse: true}, nil
+	}
+}
+
+func opToken(op *operationType) lex.Action {
+	return opTokenWithPrefs(op, nil, nil)
+}
+
+func opAssignableToken(opType *operationType, assignOpType *operationType) lex.Action {
+	return opTokenWithPrefs(opType, assignOpType, nil)
+}
+
+func assignOpToken(updateAssign bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		log.Debug("assignOpToken %v", string(m.Bytes))
+		value := string(m.Bytes)
+		op := &Operation{OperationType: assignOpType, Value: assignOpType.Type, StringValue: value, UpdateAssign: updateAssign}
+		return &token{TokenType: operationToken, Operation: op}, nil
+	}
+}
+
+func multiplyWithPrefs() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		prefs := multiplyPreferences{}
+		options := string(m.Bytes)
+		if strings.Contains(options, "+") {
+			prefs.AppendArrays = true
+		}
+		if strings.Contains(options, "?") {
+			prefs.TraversePrefs = traversePreferences{DontAutoCreate: true}
+		}
+		if strings.Contains(options, "d") {
+			prefs.DeepMergeArrays = true
+		}
+		op := &Operation{OperationType: multiplyOpType, Value: multiplyOpType.Type, StringValue: options, Preferences: prefs}
+		return &token{TokenType: operationToken, Operation: op}, nil
+	}
+}
+
+func opTokenWithPrefs(op *operationType, assignOpType *operationType, preferences interface{}) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		log.Debug("opTokenWithPrefs %v", string(m.Bytes))
+		value := string(m.Bytes)
+		op := &Operation{OperationType: op, Value: op.Type, StringValue: value, Preferences: preferences}
+		var assign *Operation
+		if assignOpType != nil {
+			assign = &Operation{OperationType: assignOpType, Value: assignOpType.Type, StringValue: value, Preferences: preferences}
+		}
+		return &token{TokenType: operationToken, Operation: op, AssignOperation: assign}, nil
+	}
+}
+
+func assignAllCommentsOp(updateAssign bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		log.Debug("assignAllCommentsOp %v", string(m.Bytes))
+		value := string(m.Bytes)
+		op := &Operation{
+			OperationType: assignCommentOpType,
+			Value:         assignCommentOpType.Type,
+			StringValue:   value,
+			UpdateAssign:  updateAssign,
+			Preferences:   commentOpPreferences{LineComment: true, HeadComment: true, FootComment: true},
+		}
+		return &token{TokenType: operationToken, Operation: op}, nil
+	}
+}
+
+func literalToken(pType tokenType, checkForPost bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		return &token{TokenType: pType, CheckForPostTraverse: checkForPost, Match: m}, nil
+	}
+}
+
+func unwrap(value string) string {
+	return value[1 : len(value)-1]
+}
+
+func numberValue() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		var numberString = string(m.Bytes)
+		var number, errParsingInt = strconv.ParseInt(numberString, 10, 64) // nolint
+		if errParsingInt != nil {
+			return nil, errParsingInt
+		}
+
+		return &token{TokenType: operationToken, Operation: createValueOperation(number, numberString)}, nil
+	}
+}
+
+func floatValue() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		var numberString = string(m.Bytes)
+		var number, errParsingInt = strconv.ParseFloat(numberString, 64) // nolint
+		if errParsingInt != nil {
+			return nil, errParsingInt
+		}
+		return &token{TokenType: operationToken, Operation: createValueOperation(number, numberString)}, nil
+	}
+}
+
+func booleanValue(val bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		return &token{TokenType: operationToken, Operation: createValueOperation(val, string(m.Bytes))}, nil
+	}
+}
+
+func stringValue(wrapped bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		value := string(m.Bytes)
+		if wrapped {
+			value = unwrap(value)
+		}
+		value = strings.ReplaceAll(value, "\\\"", "\"")
+		return &token{TokenType: operationToken, Operation: createValueOperation(value, value)}, nil
+	}
+}
+
+func getVariableOpToken() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		value := string(m.Bytes)
+
+		value = value[1:]
+
+		getVarOperation := createValueOperation(value, value)
+		getVarOperation.OperationType = getVariableOpType
+
+		return &token{TokenType: operationToken, Operation: getVarOperation, CheckForPostTraverse: true}, nil
+	}
+}
+
+func envOp(strenv bool) lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		value := string(m.Bytes)
+		preferences := envOpPreferences{}
+
+		if strenv {
+			// strenv( )
+			value = value[7 : len(value)-1]
+			preferences.StringValue = true
+		} else {
+			//env( )
+			value = value[4 : len(value)-1]
+		}
+
+		envOperation := createValueOperation(value, value)
+		envOperation.OperationType = envOpType
+		envOperation.Preferences = preferences
+
+		return &token{TokenType: operationToken, Operation: envOperation}, nil
+	}
+}
+
+func nullValue() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		return &token{TokenType: operationToken, Operation: createValueOperation(nil, string(m.Bytes))}, nil
+	}
+}
+
+func selfToken() lex.Action {
+	return func(s *lex.Scanner, m *machines.Match) (interface{}, error) {
+		op := &Operation{OperationType: selfReferenceOpType}
+		return &token{TokenType: operationToken, Operation: op}, nil
+	}
+}
+
+func initLexer() (*lex.Lexer, error) {
+	lexer := lex.NewLexer()
+	lexer.Add([]byte(`\(`), literalToken(openBracket, false))
+	lexer.Add([]byte(`\)`), literalToken(closeBracket, true))
+
+	lexer.Add([]byte(`\.\[`), literalToken(traverseArrayCollect, false))
+	lexer.Add([]byte(`\.\.`), opTokenWithPrefs(recursiveDescentOpType, nil, recursiveDescentPreferences{RecurseArray: true,
+		TraversePreferences: traversePreferences{DontFollowAlias: true, IncludeMapKeys: false}}))
+
+	lexer.Add([]byte(`\.\.\.`), opTokenWithPrefs(recursiveDescentOpType, nil, recursiveDescentPreferences{RecurseArray: true,
+		TraversePreferences: traversePreferences{DontFollowAlias: true, IncludeMapKeys: true}}))
+
+	lexer.Add([]byte(`,`), opToken(unionOpType))
+	lexer.Add([]byte(`:\s*`), opToken(createMapOpType))
+	lexer.Add([]byte(`length`), opToken(lengthOpType))
+	lexer.Add([]byte(`sortKeys`), opToken(sortKeysOpType))
+	lexer.Add([]byte(`select`), opToken(selectOpType))
+	lexer.Add([]byte(`has`), opToken(hasOpType))
+	lexer.Add([]byte(`unique`), opToken(uniqueOpType))
+	lexer.Add([]byte(`unique_by`), opToken(uniqueByOpType))
+	lexer.Add([]byte(`explode`), opToken(explodeOpType))
+	lexer.Add([]byte(`or`), opToken(orOpType))
+	lexer.Add([]byte(`and`), opToken(andOpType))
+	lexer.Add([]byte(`not`), opToken(notOpType))
+	lexer.Add([]byte(`ireduce`), opToken(reduceOpType))
+	lexer.Add([]byte(`;`), opToken(blockOpType))
+	lexer.Add([]byte(`\/\/`), opToken(alternativeOpType))
+
+	lexer.Add([]byte(`documentIndex`), opToken(getDocumentIndexOpType))
+	lexer.Add([]byte(`di`), opToken(getDocumentIndexOpType))
+	lexer.Add([]byte(`splitDoc`), opToken(splitDocumentOpType))
+
+	lexer.Add([]byte(`join`), opToken(joinStringOpType))
+	lexer.Add([]byte(`sub`), opToken(subStringOpType))
+
+	lexer.Add([]byte(`any`), opToken(anyOpType))
+	lexer.Add([]byte(`any_c`), opToken(anyConditionOpType))
+	lexer.Add([]byte(`all`), opToken(allOpType))
+	lexer.Add([]byte(`all_c`), opToken(allConditionOpType))
+
+	lexer.Add([]byte(`split`), opToken(splitStringOpType))
+	lexer.Add([]byte(`keys`), opToken(keysOpType))
+
+	lexer.Add([]byte(`style`), opAssignableToken(getStyleOpType, assignStyleOpType))
+
+	lexer.Add([]byte(`tag`), opAssignableToken(getTagOpType, assignTagOpType))
+	lexer.Add([]byte(`anchor`), opAssignableToken(getAnchorOpType, assignAnchorOpType))
+	lexer.Add([]byte(`alias`), opAssignableToken(getAliasOptype, assignAliasOpType))
+	lexer.Add([]byte(`filename`), opToken(getFilenameOpType))
+	lexer.Add([]byte(`fileIndex`), opToken(getFileIndexOpType))
+	lexer.Add([]byte(`fi`), opToken(getFileIndexOpType))
+	lexer.Add([]byte(`path`), opToken(getPathOpType))
+	lexer.Add([]byte(`to_entries`), opToken(toEntriesOpType))
+	lexer.Add([]byte(`from_entries`), opToken(fromEntriesOpType))
+	lexer.Add([]byte(`with_entries`), opToken(withEntriesOpType))
+
+	lexer.Add([]byte(`lineComment`), opTokenWithPrefs(getCommentOpType, assignCommentOpType, commentOpPreferences{LineComment: true}))
+
+	lexer.Add([]byte(`headComment`), opTokenWithPrefs(getCommentOpType, assignCommentOpType, commentOpPreferences{HeadComment: true}))
+
+	lexer.Add([]byte(`footComment`), opTokenWithPrefs(getCommentOpType, assignCommentOpType, commentOpPreferences{FootComment: true}))
+
+	lexer.Add([]byte(`comments\s*=`), assignAllCommentsOp(false))
+	lexer.Add([]byte(`comments\s*\|=`), assignAllCommentsOp(true))
+
+	lexer.Add([]byte(`collect`), opToken(collectOpType))
+
+	lexer.Add([]byte(`\s*==\s*`), opToken(equalsOpType))
+	lexer.Add([]byte(`\s*!=\s*`), opToken(notEqualsOpType))
+	lexer.Add([]byte(`\s*=\s*`), assignOpToken(false))
+
+	lexer.Add([]byte(`del`), opToken(deleteChildOpType))
+
+	lexer.Add([]byte(`\s*\|=\s*`), assignOpToken(true))
+
+	lexer.Add([]byte("( |\t|\n|\r)+"), skip)
+
+	lexer.Add([]byte(`\."[^ "]+"\??`), pathToken(true))
+	lexer.Add([]byte(`\.[^ \}\{\:\[\],\|\.\[\(\)=]+\??`), pathToken(false))
+	lexer.Add([]byte(`\.`), selfToken())
+
+	lexer.Add([]byte(`\|`), opToken(pipeOpType))
+
+	lexer.Add([]byte(`-?\d+(\.\d+)`), floatValue())
+	lexer.Add([]byte(`-?[1-9](\.\d+)?[Ee][-+]?\d+`), floatValue())
+	lexer.Add([]byte(`-?\d+`), numberValue())
+
+	lexer.Add([]byte(`[Tt][Rr][Uu][Ee]`), booleanValue(true))
+	lexer.Add([]byte(`[Ff][Aa][Ll][Ss][Ee]`), booleanValue(false))
+
+	lexer.Add([]byte(`[Nn][Uu][Ll][Ll]`), nullValue())
+	lexer.Add([]byte(`~`), nullValue())
+
+	lexer.Add([]byte(`"([^"\\]*(\\.[^"\\]*)*)"`), stringValue(true))
+	lexer.Add([]byte(`strenv\([^\)]+\)`), envOp(true))
+	lexer.Add([]byte(`env\([^\)]+\)`), envOp(false))
+
+	lexer.Add([]byte(`\[`), literalToken(openCollect, false))
+	lexer.Add([]byte(`\]\??`), literalToken(closeCollect, true))
+	lexer.Add([]byte(`\{`), literalToken(openCollectObject, false))
+	lexer.Add([]byte(`\}`), literalToken(closeCollectObject, true))
+	lexer.Add([]byte(`\*[\+|\?d]*`), multiplyWithPrefs())
+	lexer.Add([]byte(`\+`), opToken(addOpType))
+	lexer.Add([]byte(`\+=`), opToken(addAssignOpType))
+	lexer.Add([]byte(`\-`), opToken(subtractOpType))
+	lexer.Add([]byte(`\-=`), opToken(subtractAssignOpType))
+	lexer.Add([]byte(`\$[a-zA-Z_-0-9]+`), getVariableOpToken())
+	lexer.Add([]byte(`as`), opToken(assignVariableOpType))
+
+	err := lexer.CompileNFA()
+	if err != nil {
+		return nil, err
+	}
+	return lexer, nil
+}
+
+type expressionTokeniser interface {
+	Tokenise(expression string) ([]*token, error)
+}
+
+type expressionTokeniserImpl struct {
+	lexer *lex.Lexer
+}
+
+func newExpressionTokeniser() expressionTokeniser {
+	var lexer, err = initLexer()
+	if err != nil {
+		panic(err)
+	}
+	return &expressionTokeniserImpl{lexer}
+}
+
+func (p *expressionTokeniserImpl) Tokenise(expression string) ([]*token, error) {
+	scanner, err := p.lexer.Scanner([]byte(expression))
+
+	if err != nil {
+		return nil, fmt.Errorf("Parsing expression: %v", err)
+	}
+	var tokens []*token
+	for tok, err, eof := scanner.Next(); !eof; tok, err, eof = scanner.Next() {
+
+		if tok != nil {
+			currentToken := tok.(*token)
+			log.Debugf("Tokenising %v", currentToken.toString(true))
+			tokens = append(tokens, currentToken)
+		}
+		if err != nil {
+			return nil, fmt.Errorf("Parsing expression: %v", err)
+		}
+	}
+	var postProcessedTokens = make([]*token, 0)
+
+	skipNextToken := false
+
+	for index := range tokens {
+		if skipNextToken {
+			skipNextToken = false
+		} else {
+			postProcessedTokens, skipNextToken = p.handleToken(tokens, index, postProcessedTokens)
+		}
+	}
+
+	return postProcessedTokens, nil
+}
+
+func (p *expressionTokeniserImpl) handleToken(tokens []*token, index int, postProcessedTokens []*token) (tokensAccum []*token, skipNextToken bool) {
+	skipNextToken = false
+	currentToken := tokens[index]
+
+	log.Debug("processing %v", currentToken.toString(true))
+
+	if currentToken.TokenType == traverseArrayCollect {
+		//need to put a traverse array then a collect currentToken
+		// do this by adding traverse then converting currentToken to collect
+
+		if index == 0 || tokens[index-1].TokenType != operationToken ||
+			tokens[index-1].Operation.OperationType != traversePathOpType {
+			log.Debug("  adding self")
+			op := &Operation{OperationType: selfReferenceOpType, StringValue: "SELF"}
+			postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
+		}
+		log.Debug("  adding traverse array")
+		op := &Operation{OperationType: traverseArrayOpType, StringValue: "TRAVERSE_ARRAY"}
+		postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
+
+		currentToken = &token{TokenType: openCollect}
+
+	}
+
+	if index != len(tokens)-1 && currentToken.AssignOperation != nil &&
+		tokens[index+1].TokenType == operationToken &&
+		tokens[index+1].Operation.OperationType == assignOpType {
+		log.Debug("  its an update assign")
+		currentToken.Operation = currentToken.AssignOperation
+		currentToken.Operation.UpdateAssign = tokens[index+1].Operation.UpdateAssign
+		skipNextToken = true
+	}
+
+	log.Debug("  adding token to the fixed list")
+	postProcessedTokens = append(postProcessedTokens, currentToken)
+
+	if index != len(tokens)-1 &&
+		((currentToken.TokenType == openCollect && tokens[index+1].TokenType == closeCollect) ||
+			(currentToken.TokenType == openCollectObject && tokens[index+1].TokenType == closeCollectObject)) {
+		log.Debug("  adding empty")
+		op := &Operation{OperationType: emptyOpType, StringValue: "EMPTY"}
+		postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
+	}
+
+	if index != len(tokens)-1 && currentToken.CheckForPostTraverse &&
+		tokens[index+1].TokenType == operationToken &&
+		tokens[index+1].Operation.OperationType == traversePathOpType {
+		log.Debug("  adding pipe because the next thing is traverse")
+		op := &Operation{OperationType: shortPipeOpType, Value: "PIPE"}
+		postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
+	}
+	if index != len(tokens)-1 && currentToken.CheckForPostTraverse &&
+		tokens[index+1].TokenType == openCollect {
+
+		// if tokens[index].TokenType == closeCollect {
+		// 	log.Debug("  adding pipe because next is opencollect")
+		// 	op := &Operation{OperationType: shortPipeOpType, Value: "PIPE"}
+		// 	postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
+		// }
+		log.Debug("  adding traverArray because next is opencollect")
+		op := &Operation{OperationType: traverseArrayOpType}
+		postProcessedTokens = append(postProcessedTokens, &token{TokenType: operationToken, Operation: op})
+	}
+	return postProcessedTokens, skipNextToken
+}

pkg/yqlib/lib.go

@@ -1,3 +1,5 @@
+// Use the top level Evaluator or StreamEvaluator to evaluate expressions and return matches.
+//
 package yqlib
 
 import (
@@ -11,77 +13,108 @@ import (
 
 var log = logging.MustGetLogger("yq-lib")
 
-type OperationType struct {
+type operationType struct {
 	Type       string
 	NumArgs    uint // number of arguments to the op
 	Precedence uint
-	Handler    OperatorHandler
+	Handler    operatorHandler
 }
 
-// operators TODO:
-// - cookbook doc for common things
-// - mergeEmpty (sets only if the document is empty, do I do that now?)
+var orOpType = &operationType{Type: "OR", NumArgs: 2, Precedence: 20, Handler: orOperator}
+var andOpType = &operationType{Type: "AND", NumArgs: 2, Precedence: 20, Handler: andOperator}
+var reduceOpType = &operationType{Type: "REDUCE", NumArgs: 2, Precedence: 35, Handler: reduceOperator}
 
-var Or = &OperationType{Type: "OR", NumArgs: 2, Precedence: 20, Handler: OrOperator}
-var And = &OperationType{Type: "AND", NumArgs: 2, Precedence: 20, Handler: AndOperator}
+var blockOpType = &operationType{Type: "BLOCK", Precedence: 10, NumArgs: 2, Handler: emptyOperator}
 
-var Union = &OperationType{Type: "UNION", NumArgs: 2, Precedence: 10, Handler: UnionOperator}
+var unionOpType = &operationType{Type: "UNION", NumArgs: 2, Precedence: 10, Handler: unionOperator}
 
-var Pipe = &OperationType{Type: "PIPE", NumArgs: 2, Precedence: 30, Handler: PipeOperator}
+var pipeOpType = &operationType{Type: "PIPE", NumArgs: 2, Precedence: 30, Handler: pipeOperator}
 
-var Assign = &OperationType{Type: "ASSIGN", NumArgs: 2, Precedence: 40, Handler: AssignUpdateOperator}
-var AddAssign = &OperationType{Type: "ADD_ASSIGN", NumArgs: 2, Precedence: 40, Handler: AddAssignOperator}
+var assignOpType = &operationType{Type: "ASSIGN", NumArgs: 2, Precedence: 40, Handler: assignUpdateOperator}
+var addAssignOpType = &operationType{Type: "ADD_ASSIGN", NumArgs: 2, Precedence: 40, Handler: addAssignOperator}
+var subtractAssignOpType = &operationType{Type: "SUBTRACT_ASSIGN", NumArgs: 2, Precedence: 40, Handler: subtractAssignOperator}
 
-var AssignAttributes = &OperationType{Type: "ASSIGN_ATTRIBUTES", NumArgs: 2, Precedence: 40, Handler: AssignAttributesOperator}
-var AssignStyle = &OperationType{Type: "ASSIGN_STYLE", NumArgs: 2, Precedence: 40, Handler: AssignStyleOperator}
-var AssignTag = &OperationType{Type: "ASSIGN_TAG", NumArgs: 2, Precedence: 40, Handler: AssignTagOperator}
-var AssignComment = &OperationType{Type: "ASSIGN_COMMENT", NumArgs: 2, Precedence: 40, Handler: AssignCommentsOperator}
+var assignAttributesOpType = &operationType{Type: "ASSIGN_ATTRIBUTES", NumArgs: 2, Precedence: 40, Handler: assignAttributesOperator}
+var assignStyleOpType = &operationType{Type: "ASSIGN_STYLE", NumArgs: 2, Precedence: 40, Handler: assignStyleOperator}
+var assignVariableOpType = &operationType{Type: "ASSIGN_VARIABLE", NumArgs: 2, Precedence: 40, Handler: assignVariableOperator}
+var assignTagOpType = &operationType{Type: "ASSIGN_TAG", NumArgs: 2, Precedence: 40, Handler: assignTagOperator}
+var assignCommentOpType = &operationType{Type: "ASSIGN_COMMENT", NumArgs: 2, Precedence: 40, Handler: assignCommentsOperator}
+var assignAnchorOpType = &operationType{Type: "ASSIGN_ANCHOR", NumArgs: 2, Precedence: 40, Handler: assignAnchorOperator}
+var assignAliasOpType = &operationType{Type: "ASSIGN_ALIAS", NumArgs: 2, Precedence: 40, Handler: assignAliasOperator}
 
-var Multiply = &OperationType{Type: "MULTIPLY", NumArgs: 2, Precedence: 45, Handler: MultiplyOperator}
-var Add = &OperationType{Type: "ADD", NumArgs: 2, Precedence: 45, Handler: AddOperator}
+var multiplyOpType = &operationType{Type: "MULTIPLY", NumArgs: 2, Precedence: 42, Handler: multiplyOperator}
+var addOpType = &operationType{Type: "ADD", NumArgs: 2, Precedence: 42, Handler: addOperator}
+var subtractOpType = &operationType{Type: "SUBTRACT", NumArgs: 2, Precedence: 42, Handler: subtractOperator}
+var alternativeOpType = &operationType{Type: "ALTERNATIVE", NumArgs: 2, Precedence: 42, Handler: alternativeOperator}
 
-var Equals = &OperationType{Type: "EQUALS", NumArgs: 2, Precedence: 40, Handler: EqualsOperator}
-var CreateMap = &OperationType{Type: "CREATE_MAP", NumArgs: 2, Precedence: 40, Handler: CreateMapOperator}
+var equalsOpType = &operationType{Type: "EQUALS", NumArgs: 2, Precedence: 40, Handler: equalsOperator}
+var notEqualsOpType = &operationType{Type: "EQUALS", NumArgs: 2, Precedence: 40, Handler: notEqualsOperator}
 
-var ShortPipe = &OperationType{Type: "SHORT_PIPE", NumArgs: 2, Precedence: 45, Handler: PipeOperator}
+//createmap needs to be above union, as we use union to build the components of the objects
+var createMapOpType = &operationType{Type: "CREATE_MAP", NumArgs: 2, Precedence: 15, Handler: createMapOperator}
 
-var Length = &OperationType{Type: "LENGTH", NumArgs: 0, Precedence: 50, Handler: LengthOperator}
-var Collect = &OperationType{Type: "COLLECT", NumArgs: 0, Precedence: 50, Handler: CollectOperator}
-var GetStyle = &OperationType{Type: "GET_STYLE", NumArgs: 0, Precedence: 50, Handler: GetStyleOperator}
-var GetTag = &OperationType{Type: "GET_TAG", NumArgs: 0, Precedence: 50, Handler: GetTagOperator}
-var GetComment = &OperationType{Type: "GET_COMMENT", NumArgs: 0, Precedence: 50, Handler: GetCommentsOperator}
-var GetDocumentIndex = &OperationType{Type: "GET_DOCUMENT_INDEX", NumArgs: 0, Precedence: 50, Handler: GetDocumentIndexOperator}
-var GetFilename = &OperationType{Type: "GET_FILENAME", NumArgs: 0, Precedence: 50, Handler: GetFilenameOperator}
-var GetFileIndex = &OperationType{Type: "GET_FILE_INDEX", NumArgs: 0, Precedence: 50, Handler: GetFileIndexOperator}
-var GetPath = &OperationType{Type: "GET_PATH", NumArgs: 0, Precedence: 50, Handler: GetPathOperator}
+var shortPipeOpType = &operationType{Type: "SHORT_PIPE", NumArgs: 2, Precedence: 45, Handler: pipeOperator}
 
-var Explode = &OperationType{Type: "EXPLODE", NumArgs: 1, Precedence: 50, Handler: ExplodeOperator}
-var SortKeys = &OperationType{Type: "SORT_KEYS", NumArgs: 1, Precedence: 50, Handler: SortKeysOperator}
+var lengthOpType = &operationType{Type: "LENGTH", NumArgs: 0, Precedence: 50, Handler: lengthOperator}
+var collectOpType = &operationType{Type: "COLLECT", NumArgs: 0, Precedence: 50, Handler: collectOperator}
 
-var CollectObject = &OperationType{Type: "COLLECT_OBJECT", NumArgs: 0, Precedence: 50, Handler: CollectObjectOperator}
-var TraversePath = &OperationType{Type: "TRAVERSE_PATH", NumArgs: 0, Precedence: 50, Handler: TraversePathOperator}
+var anyOpType = &operationType{Type: "ANY", NumArgs: 0, Precedence: 50, Handler: anyOperator}
+var allOpType = &operationType{Type: "ALL", NumArgs: 0, Precedence: 50, Handler: allOperator}
+var anyConditionOpType = &operationType{Type: "ANY_CONDITION", NumArgs: 1, Precedence: 50, Handler: anyOperator}
+var allConditionOpType = &operationType{Type: "ALL_CONDITION", NumArgs: 1, Precedence: 50, Handler: allOperator}
 
-var DocumentFilter = &OperationType{Type: "DOCUMENT_FILTER", NumArgs: 0, Precedence: 50, Handler: TraversePathOperator}
-var SelfReference = &OperationType{Type: "SELF", NumArgs: 0, Precedence: 50, Handler: SelfOperator}
-var ValueOp = &OperationType{Type: "VALUE", NumArgs: 0, Precedence: 50, Handler: ValueOperator}
-var Not = &OperationType{Type: "NOT", NumArgs: 0, Precedence: 50, Handler: NotOperator}
-var Empty = &OperationType{Type: "EMPTY", NumArgs: 50, Handler: EmptyOperator}
+var toEntriesOpType = &operationType{Type: "TO_ENTRIES", NumArgs: 0, Precedence: 50, Handler: toEntriesOperator}
+var fromEntriesOpType = &operationType{Type: "FROM_ENTRIES", NumArgs: 0, Precedence: 50, Handler: fromEntriesOperator}
+var withEntriesOpType = &operationType{Type: "WITH_ENTRIES", NumArgs: 1, Precedence: 50, Handler: withEntriesOperator}
 
-var RecursiveDescent = &OperationType{Type: "RECURSIVE_DESCENT", NumArgs: 0, Precedence: 50, Handler: RecursiveDescentOperator}
+var splitDocumentOpType = &operationType{Type: "SPLIT_DOC", NumArgs: 0, Precedence: 50, Handler: splitDocumentOperator}
+var getVariableOpType = &operationType{Type: "GET_VARIABLE", NumArgs: 0, Precedence: 55, Handler: getVariableOperator}
+var getStyleOpType = &operationType{Type: "GET_STYLE", NumArgs: 0, Precedence: 50, Handler: getStyleOperator}
+var getTagOpType = &operationType{Type: "GET_TAG", NumArgs: 0, Precedence: 50, Handler: getTagOperator}
+var getCommentOpType = &operationType{Type: "GET_COMMENT", NumArgs: 0, Precedence: 50, Handler: getCommentsOperator}
+var getAnchorOpType = &operationType{Type: "GET_ANCHOR", NumArgs: 0, Precedence: 50, Handler: getAnchorOperator}
+var getAliasOptype = &operationType{Type: "GET_ALIAS", NumArgs: 0, Precedence: 50, Handler: getAliasOperator}
+var getDocumentIndexOpType = &operationType{Type: "GET_DOCUMENT_INDEX", NumArgs: 0, Precedence: 50, Handler: getDocumentIndexOperator}
+var getFilenameOpType = &operationType{Type: "GET_FILENAME", NumArgs: 0, Precedence: 50, Handler: getFilenameOperator}
+var getFileIndexOpType = &operationType{Type: "GET_FILE_INDEX", NumArgs: 0, Precedence: 50, Handler: getFileIndexOperator}
+var getPathOpType = &operationType{Type: "GET_PATH", NumArgs: 0, Precedence: 50, Handler: getPathOperator}
 
-var Select = &OperationType{Type: "SELECT", NumArgs: 1, Precedence: 50, Handler: SelectOperator}
-var Has = &OperationType{Type: "HAS", NumArgs: 1, Precedence: 50, Handler: HasOperator}
-var DeleteChild = &OperationType{Type: "DELETE", NumArgs: 1, Precedence: 40, Handler: DeleteChildOperator}
+var explodeOpType = &operationType{Type: "EXPLODE", NumArgs: 1, Precedence: 50, Handler: explodeOperator}
+var sortKeysOpType = &operationType{Type: "SORT_KEYS", NumArgs: 1, Precedence: 50, Handler: sortKeysOperator}
+var joinStringOpType = &operationType{Type: "JOIN", NumArgs: 1, Precedence: 50, Handler: joinStringOperator}
+var subStringOpType = &operationType{Type: "SUBSTR", NumArgs: 1, Precedence: 50, Handler: substituteStringOperator}
+var splitStringOpType = &operationType{Type: "SPLIT", NumArgs: 1, Precedence: 50, Handler: splitStringOperator}
+
+var keysOpType = &operationType{Type: "KEYS", NumArgs: 0, Precedence: 50, Handler: keysOperator}
+
+var collectObjectOpType = &operationType{Type: "COLLECT_OBJECT", NumArgs: 0, Precedence: 50, Handler: collectObjectOperator}
+var traversePathOpType = &operationType{Type: "TRAVERSE_PATH", NumArgs: 0, Precedence: 55, Handler: traversePathOperator}
+var traverseArrayOpType = &operationType{Type: "TRAVERSE_ARRAY", NumArgs: 2, Precedence: 50, Handler: traverseArrayOperator}
+
+var selfReferenceOpType = &operationType{Type: "SELF", NumArgs: 0, Precedence: 55, Handler: selfOperator}
+var valueOpType = &operationType{Type: "VALUE", NumArgs: 0, Precedence: 50, Handler: valueOperator}
+var envOpType = &operationType{Type: "ENV", NumArgs: 0, Precedence: 50, Handler: envOperator}
+var notOpType = &operationType{Type: "NOT", NumArgs: 0, Precedence: 50, Handler: notOperator}
+var emptyOpType = &operationType{Type: "EMPTY", Precedence: 50, Handler: emptyOperator}
+
+var recursiveDescentOpType = &operationType{Type: "RECURSIVE_DESCENT", NumArgs: 0, Precedence: 50, Handler: recursiveDescentOperator}
+
+var selectOpType = &operationType{Type: "SELECT", NumArgs: 1, Precedence: 50, Handler: selectOperator}
+var hasOpType = &operationType{Type: "HAS", NumArgs: 1, Precedence: 50, Handler: hasOperator}
+var uniqueOpType = &operationType{Type: "UNIQUE", NumArgs: 0, Precedence: 50, Handler: unique}
+var uniqueByOpType = &operationType{Type: "UNIQUE_BY", NumArgs: 1, Precedence: 50, Handler: uniqueBy}
+var deleteChildOpType = &operationType{Type: "DELETE", NumArgs: 1, Precedence: 40, Handler: deleteChildOperator}
 
 type Operation struct {
-	OperationType *OperationType
+	OperationType *operationType
 	Value         interface{}
 	StringValue   string
 	CandidateNode *CandidateNode // used for Value Path elements
 	Preferences   interface{}
+	UpdateAssign  bool // used for assign ops, when true it means we evaluate the rhs given the lhs
 }
 
-func CreateValueOperation(value interface{}, stringValue string) *Operation {
+func createValueOperation(value interface{}, stringValue string) *Operation {
 	var node yaml.Node = yaml.Node{Kind: yaml.ScalarNode}
 	node.Value = stringValue
 
@@ -99,7 +132,7 @@ func CreateValueOperation(value interface{}, stringValue string) *Operation {
 	}
 
 	return &Operation{
-		OperationType: ValueOp,
+		OperationType: valueOpType,
 		Value:         value,
 		StringValue:   stringValue,
 		CandidateNode: &CandidateNode{Node: &node},
@@ -108,13 +141,11 @@ func CreateValueOperation(value interface{}, stringValue string) *Operation {
 
 // debugging purposes only
 func (p *Operation) toString() string {
-	if p.OperationType == TraversePath {
+	if p.OperationType == traversePathOpType {
 		return fmt.Sprintf("%v", p.Value)
-	} else if p.OperationType == DocumentFilter {
-		return fmt.Sprintf("d%v", p.Value)
-	} else if p.OperationType == SelfReference {
+	} else if p.OperationType == selfReferenceOpType {
 		return "SELF"
-	} else if p.OperationType == ValueOp {
+	} else if p.OperationType == valueOpType {
 		return fmt.Sprintf("%v (%T)", p.Value, p.Value)
 	} else {
 		return fmt.Sprintf("%v", p.OperationType.Type)

pkg/yqlib/matchKeyString.go

@@ -1,6 +1,6 @@
 package yqlib
 
-func Match(name string, pattern string) (matched bool) {
+func matchKey(name string, pattern string) (matched bool) {
 	if pattern == "" {
 		return name == pattern
 	}

pkg/yqlib/operator_add.go

@@ -3,32 +3,26 @@ package yqlib
 import (
 	"fmt"
 
-	"container/list"
+	"strconv"
 
 	yaml "gopkg.in/yaml.v3"
 )
 
-func createSelfAddOp(rhs *PathTreeNode) *PathTreeNode {
-	return &PathTreeNode{Operation: &Operation{OperationType: Add},
-		Lhs: &PathTreeNode{Operation: &Operation{OperationType: SelfReference}},
+func createAddOp(lhs *ExpressionNode, rhs *ExpressionNode) *ExpressionNode {
+	return &ExpressionNode{Operation: &Operation{OperationType: addOpType},
+		Lhs: lhs,
 		Rhs: rhs}
 }
 
-func AddAssignOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	assignmentOp := &Operation{OperationType: Assign}
-	assignmentOp.Preferences = &AssignOpPreferences{true}
-
-	assignmentOpNode := &PathTreeNode{Operation: assignmentOp, Lhs: pathNode.Lhs, Rhs: createSelfAddOp(pathNode.Rhs)}
-	return d.GetMatchingNodes(matchingNodes, assignmentOpNode)
+func addAssignOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	assignmentOp := &Operation{OperationType: assignOpType}
+	assignmentOp.UpdateAssign = true
+	selfExpression := &ExpressionNode{Operation: &Operation{OperationType: selfReferenceOpType}}
+	assignmentOpNode := &ExpressionNode{Operation: assignmentOp, Lhs: expressionNode.Lhs, Rhs: createAddOp(selfExpression, expressionNode.Rhs)}
+	return d.GetMatchingNodes(context, assignmentOpNode)
 }
 
-func toNodes(candidates *list.List) []*yaml.Node {
-
-	if candidates.Len() == 0 {
-		return []*yaml.Node{}
-	}
-	candidate := candidates.Front().Value.(*CandidateNode)
-
+func toNodes(candidate *CandidateNode) []*yaml.Node {
 	if candidate.Node.Tag == "!!null" {
 		return []*yaml.Node{}
 	}
@@ -42,42 +36,76 @@ func toNodes(candidates *list.List) []*yaml.Node {
 
 }
 
-func AddOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func addOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("Add operator")
-	var results = list.New()
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
-	if err != nil {
-		return nil, err
-	}
-	rhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
 
-	if err != nil {
-		return nil, err
-	}
-
-	for el := lhs.Front(); el != nil; el = el.Next() {
-		lhsCandidate := el.Value.(*CandidateNode)
-		lhsNode := UnwrapDoc(lhsCandidate.Node)
-
-		target := &CandidateNode{
-			Path:     lhsCandidate.Path,
-			Document: lhsCandidate.Document,
-			Filename: lhsCandidate.Filename,
-			Node:     &yaml.Node{},
-		}
-
-		switch lhsNode.Kind {
-		case yaml.MappingNode:
-			return nil, fmt.Errorf("Maps not yet supported for addition")
-		case yaml.SequenceNode:
-			target.Node.Kind = yaml.SequenceNode
-			target.Node.Style = lhsNode.Style
-			target.Node.Tag = "!!seq"
-			target.Node.Content = append(lhsNode.Content, toNodes(rhs)...)
-			results.PushBack(target)
-		case yaml.ScalarNode:
-			return nil, fmt.Errorf("Scalars not yet supported for addition")
-		}
-	}
-	return results, nil
+	return crossFunction(d, context.ReadOnlyClone(), expressionNode, add, false)
+}
+
+func add(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+	lhs.Node = unwrapDoc(lhs.Node)
+	rhs.Node = unwrapDoc(rhs.Node)
+
+	lhsNode := lhs.Node
+
+	if lhsNode.Tag == "!!null" {
+		return lhs.CreateChild(nil, rhs.Node), nil
+	}
+
+	target := lhs.CreateChild(nil, &yaml.Node{})
+
+	switch lhsNode.Kind {
+	case yaml.MappingNode:
+		return nil, fmt.Errorf("Maps not yet supported for addition")
+	case yaml.SequenceNode:
+		target.Node.Kind = yaml.SequenceNode
+		target.Node.Style = lhsNode.Style
+		target.Node.Tag = "!!seq"
+		target.Node.Content = append(lhsNode.Content, toNodes(rhs)...)
+	case yaml.ScalarNode:
+		if rhs.Node.Kind != yaml.ScalarNode {
+			return nil, fmt.Errorf("%v (%v) cannot be added to a %v", rhs.Node.Tag, rhs.Path, lhsNode.Tag)
+		}
+		target.Node.Kind = yaml.ScalarNode
+		target.Node.Style = lhsNode.Style
+		return addScalars(target, lhsNode, rhs.Node)
+	}
+
+	return target, nil
+}
+
+func addScalars(target *CandidateNode, lhs *yaml.Node, rhs *yaml.Node) (*CandidateNode, error) {
+
+	if lhs.Tag == "!!str" {
+		target.Node.Tag = "!!str"
+		target.Node.Value = lhs.Value + rhs.Value
+	} else if lhs.Tag == "!!int" && rhs.Tag == "!!int" {
+		lhsNum, err := strconv.Atoi(lhs.Value)
+		if err != nil {
+			return nil, err
+		}
+		rhsNum, err := strconv.Atoi(rhs.Value)
+		if err != nil {
+			return nil, err
+		}
+		sum := lhsNum + rhsNum
+		target.Node.Tag = "!!int"
+		target.Node.Value = fmt.Sprintf("%v", sum)
+	} else if (lhs.Tag == "!!int" || lhs.Tag == "!!float") && (rhs.Tag == "!!int" || rhs.Tag == "!!float") {
+		lhsNum, err := strconv.ParseFloat(lhs.Value, 64)
+		if err != nil {
+			return nil, err
+		}
+		rhsNum, err := strconv.ParseFloat(rhs.Value, 64)
+		if err != nil {
+			return nil, err
+		}
+		sum := lhsNum + rhsNum
+		target.Node.Tag = "!!float"
+		target.Node.Value = fmt.Sprintf("%v", sum)
+	} else {
+		return nil, fmt.Errorf("%v cannot be added to %v", lhs.Tag, rhs.Tag)
+	}
+
+	return target, nil
 }

pkg/yqlib/operator_add_test.go

@@ -5,6 +5,31 @@ import (
 )
 
 var addOperatorScenarios = []expressionScenario{
+	{
+		skipDoc:    true,
+		document:   `[{a: foo, b: bar}, {a: 1, b: 2}]`,
+		expression: ".[] | .a + .b",
+		expected: []string{
+			"D0, P[0 a], (!!str)::foobar\n",
+			"D0, P[1 a], (!!int)::3\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{}`,
+		expression: "(.a + .b) as $x",
+		expected: []string{
+			"D0, P[], (doc)::{}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `a: 0`,
+		expression: ".a += .b.c",
+		expected: []string{
+			"D0, P[], (doc)::a: 0\n",
+		},
+	},
 	{
 		description: "Concatenate and assign arrays",
 		document:    `{a: {val: thing, b: [cat,dog]}}`,
@@ -21,6 +46,14 @@ var addOperatorScenarios = []expressionScenario{
 			"D0, P[a], (!!seq)::[1, 2, 3, 4]\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		expression: `[1] + ([2], [3])`,
+		expected: []string{
+			"D0, P[], (!!seq)::- 1\n- 2\n",
+			"D0, P[], (!!seq)::- 1\n- 3\n",
+		},
+	},
 	{
 		description: "Concatenate null to array",
 		document:    `{a: [1,2]}`,
@@ -30,11 +63,11 @@ var addOperatorScenarios = []expressionScenario{
 		},
 	},
 	{
-		description: "Add object to array",
-		document:    `{a: [1,2], c: {cat: meow}}`,
-		expression:  `.a + .c`,
+		description: "Add new object to array",
+		document:    `a: [{dog: woof}]`,
+		expression:  `.a + {"cat": "meow"}`,
 		expected: []string{
-			"D0, P[a], (!!seq)::[1, 2, {cat: meow}]\n",
+			"D0, P[a], (!!seq)::[{dog: woof}, {cat: meow}]\n",
 		},
 	},
 	{
@@ -46,13 +79,63 @@ var addOperatorScenarios = []expressionScenario{
 		},
 	},
 	{
-		description: "Update array (append)",
+		description: "Append to array",
 		document:    `{a: [1,2], b: [3,4]}`,
 		expression:  `.a = .a + .b`,
 		expected: []string{
 			"D0, P[], (doc)::{a: [1, 2, 3, 4], b: [3, 4]}\n",
 		},
 	},
+	{
+		description: "Relative append",
+		document:    `a: { a1: {b: [cat]}, a2: {b: [dog]}, a3: {} }`,
+		expression:  `.a[].b += ["mouse"]`,
+		expected: []string{
+			"D0, P[], (doc)::a: {a1: {b: [cat, mouse]}, a2: {b: [dog, mouse]}, a3: {b: [mouse]}}\n",
+		},
+	},
+	{
+		description: "String concatenation",
+		document:    `{a: cat, b: meow}`,
+		expression:  `.a = .a + .b`,
+		expected: []string{
+			"D0, P[], (doc)::{a: catmeow, b: meow}\n",
+		},
+	},
+	{
+		description:    "Number addition - float",
+		subdescription: "If the lhs or rhs are floats then the expression will be calculated with floats.",
+		document:       `{a: 3, b: 4.9}`,
+		expression:     `.a = .a + .b`,
+		expected: []string{
+			"D0, P[], (doc)::{a: 7.9, b: 4.9}\n",
+		},
+	},
+	{
+		description:    "Number addition - int",
+		subdescription: "If both the lhs and rhs are ints then the expression will be calculated with ints.",
+		document:       `{a: 3, b: 4}`,
+		expression:     `.a = .a + .b`,
+		expected: []string{
+			"D0, P[], (doc)::{a: 7, b: 4}\n",
+		},
+	},
+	{
+		description: "Increment numbers",
+		document:    `{a: 3, b: 5}`,
+		expression:  `.[] += 1`,
+		expected: []string{
+			"D0, P[], (doc)::{a: 4, b: 6}\n",
+		},
+	},
+	{
+		description:    "Add to null",
+		subdescription: "Adding to null simply returns the rhs",
+		expression:     `null + "cat"`,
+		expected: []string{
+			"D0, P[], (!!str)::cat\n",
+		},
+	},
 }
 
 func TestAddOperatorScenarios(t *testing.T) {

pkg/yqlib/operator_alternative.go

@@ -0,0 +1,24 @@
+package yqlib
+
+func alternativeOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("-- alternative")
+	return crossFunction(d, context.ReadOnlyClone(), expressionNode, alternativeFunc, true)
+}
+
+func alternativeFunc(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+	if lhs == nil {
+		return rhs, nil
+	}
+	lhs.Node = unwrapDoc(lhs.Node)
+	rhs.Node = unwrapDoc(rhs.Node)
+	log.Debugf("Alternative LHS: %v", lhs.Node.Tag)
+	log.Debugf("-          RHS: %v", rhs.Node.Tag)
+
+	isTrue, err := isTruthy(lhs)
+	if err != nil {
+		return nil, err
+	} else if isTrue {
+		return lhs, nil
+	}
+	return rhs, nil
+}

pkg/yqlib/operator_alternative_test.go

@@ -0,0 +1,84 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var alternativeOperatorScenarios = []expressionScenario{
+	{
+		skipDoc:    true,
+		expression: `.b // .c`,
+		document:   `a: bridge`,
+		expected:   []string{},
+	},
+	{
+		skipDoc:    true,
+		expression: `(.b // "hello") as $x`,
+		document:   `a: bridge`,
+		expected: []string{
+			"D0, P[], (doc)::a: bridge\n",
+		},
+	},
+	{
+		description: "LHS is defined",
+		expression:  `.a // "hello"`,
+		document:    `{a: bridge}`,
+		expected: []string{
+			"D0, P[a], (!!str)::bridge\n",
+		},
+	},
+	{
+		expression: `select(tag == "seq") // "cat"`,
+		skipDoc:    true,
+		document:   `a: frog`,
+		expected: []string{
+			"D0, P[], (!!str)::cat\n",
+		},
+	},
+	{
+		description: "LHS is not defined",
+		expression:  `.a // "hello"`,
+		document:    `{}`,
+		expected: []string{
+			"D0, P[], (!!str)::hello\n",
+		},
+	},
+	{
+		description: "LHS is null",
+		expression:  `.a // "hello"`,
+		document:    `{a: ~}`,
+		expected: []string{
+			"D0, P[], (!!str)::hello\n",
+		},
+	},
+	{
+		description: "LHS is false",
+		expression:  `.a // "hello"`,
+		document:    `{a: false}`,
+		expected: []string{
+			"D0, P[], (!!str)::hello\n",
+		},
+	},
+	{
+		description: "RHS is an expression",
+		expression:  `.a // .b`,
+		document:    `{a: false, b: cat}`,
+		expected: []string{
+			"D0, P[b], (!!str)::cat\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		expression: `false // true`,
+		expected: []string{
+			"D0, P[], (!!bool)::true\n",
+		},
+	},
+}
+
+func TestAlternativeOperatorScenarios(t *testing.T) {
+	for _, tt := range alternativeOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "Alternative (Default value)", alternativeOperatorScenarios)
+}

pkg/yqlib/operator_anchors_aliases.go

@@ -0,0 +1,263 @@
+package yqlib
+
+import (
+	"container/list"
+
+	yaml "gopkg.in/yaml.v3"
+)
+
+func assignAliasOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+
+	log.Debugf("AssignAlias operator!")
+
+	aliasName := ""
+	if !expressionNode.Operation.UpdateAssign {
+		rhs, err := d.GetMatchingNodes(context.ReadOnlyClone(), expressionNode.Rhs)
+		if err != nil {
+			return Context{}, err
+		}
+		if rhs.MatchingNodes.Front() != nil {
+			aliasName = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
+		}
+	}
+
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
+
+	if err != nil {
+		return Context{}, err
+	}
+
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		log.Debugf("Setting aliasName : %v", candidate.GetKey())
+
+		if expressionNode.Operation.UpdateAssign {
+			rhs, err := d.GetMatchingNodes(context.SingleReadonlyChildContext(candidate), expressionNode.Rhs)
+			if err != nil {
+				return Context{}, err
+			}
+			if rhs.MatchingNodes.Front() != nil {
+				aliasName = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
+			}
+		}
+
+		if aliasName != "" {
+			candidate.Node.Kind = yaml.AliasNode
+			candidate.Node.Value = aliasName
+		}
+	}
+	return context, nil
+}
+
+func getAliasOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("GetAlias operator!")
+	var results = list.New()
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		node := &yaml.Node{Kind: yaml.ScalarNode, Value: candidate.Node.Value, Tag: "!!str"}
+		result := candidate.CreateChild(nil, node)
+		results.PushBack(result)
+	}
+	return context.ChildContext(results), nil
+}
+
+func assignAnchorOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+
+	log.Debugf("AssignAnchor operator!")
+
+	anchorName := ""
+	if !expressionNode.Operation.UpdateAssign {
+		rhs, err := d.GetMatchingNodes(context.ReadOnlyClone(), expressionNode.Rhs)
+		if err != nil {
+			return Context{}, err
+		}
+
+		if rhs.MatchingNodes.Front() != nil {
+			anchorName = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
+		}
+	}
+
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
+
+	if err != nil {
+		return Context{}, err
+	}
+
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		log.Debugf("Setting anchorName of : %v", candidate.GetKey())
+
+		if expressionNode.Operation.UpdateAssign {
+			rhs, err := d.GetMatchingNodes(context.SingleReadonlyChildContext(candidate), expressionNode.Rhs)
+			if err != nil {
+				return Context{}, err
+			}
+
+			if rhs.MatchingNodes.Front() != nil {
+				anchorName = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node.Value
+			}
+		}
+
+		candidate.Node.Anchor = anchorName
+	}
+	return context, nil
+}
+
+func getAnchorOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("GetAnchor operator!")
+	var results = list.New()
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		anchor := candidate.Node.Anchor
+		node := &yaml.Node{Kind: yaml.ScalarNode, Value: anchor, Tag: "!!str"}
+		result := candidate.CreateChild(nil, node)
+		results.PushBack(result)
+	}
+	return context.ChildContext(results), nil
+}
+
+func explodeOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debugf("-- ExplodeOperation")
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+
+		rhs, err := d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
+
+		if err != nil {
+			return Context{}, err
+		}
+		for childEl := rhs.MatchingNodes.Front(); childEl != nil; childEl = childEl.Next() {
+			err = explodeNode(childEl.Value.(*CandidateNode).Node, context)
+			if err != nil {
+				return Context{}, err
+			}
+		}
+
+	}
+
+	return context, nil
+}
+
+func explodeNode(node *yaml.Node, context Context) error {
+	node.Anchor = ""
+	switch node.Kind {
+	case yaml.SequenceNode, yaml.DocumentNode:
+		for index, contentNode := range node.Content {
+			log.Debugf("exploding index %v", index)
+			errorInContent := explodeNode(contentNode, context)
+			if errorInContent != nil {
+				return errorInContent
+			}
+		}
+		return nil
+	case yaml.AliasNode:
+		log.Debugf("its an alias!")
+		if node.Alias != nil {
+			node.Kind = node.Alias.Kind
+			node.Style = node.Alias.Style
+			node.Tag = node.Alias.Tag
+			node.Content = node.Alias.Content
+			node.Value = node.Alias.Value
+			node.Alias = nil
+		}
+		return nil
+	case yaml.MappingNode:
+		var newContent = list.New()
+		for index := 0; index < len(node.Content); index = index + 2 {
+			keyNode := node.Content[index]
+			valueNode := node.Content[index+1]
+			log.Debugf("traversing %v", keyNode.Value)
+			if keyNode.Value != "<<" {
+				err := overrideEntry(node, keyNode, valueNode, index, context.ChildContext(newContent))
+				if err != nil {
+					return err
+				}
+			} else {
+				if valueNode.Kind == yaml.SequenceNode {
+					log.Debugf("an alias merge list!")
+					for index := len(valueNode.Content) - 1; index >= 0; index = index - 1 {
+						aliasNode := valueNode.Content[index]
+						err := applyAlias(node, aliasNode.Alias, index, context.ChildContext(newContent))
+						if err != nil {
+							return err
+						}
+					}
+				} else {
+					log.Debugf("an alias merge!")
+					err := applyAlias(node, valueNode.Alias, index, context.ChildContext(newContent))
+					if err != nil {
+						return err
+					}
+				}
+			}
+		}
+		node.Content = make([]*yaml.Node, newContent.Len())
+		index := 0
+		for newEl := newContent.Front(); newEl != nil; newEl = newEl.Next() {
+			node.Content[index] = newEl.Value.(*yaml.Node)
+			index++
+		}
+
+		return nil
+	default:
+		return nil
+	}
+}
+
+func applyAlias(node *yaml.Node, alias *yaml.Node, aliasIndex int, newContent Context) error {
+	if alias == nil {
+		return nil
+	}
+	for index := 0; index < len(alias.Content); index = index + 2 {
+		keyNode := alias.Content[index]
+		log.Debugf("applying alias key %v", keyNode.Value)
+		valueNode := alias.Content[index+1]
+		err := overrideEntry(node, keyNode, valueNode, aliasIndex, newContent)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func overrideEntry(node *yaml.Node, key *yaml.Node, value *yaml.Node, startIndex int, newContent Context) error {
+
+	err := explodeNode(value, newContent)
+
+	if err != nil {
+		return err
+	}
+
+	for newEl := newContent.MatchingNodes.Front(); newEl != nil; newEl = newEl.Next() {
+		valueEl := newEl.Next() // move forward twice
+		keyNode := newEl.Value.(*yaml.Node)
+		log.Debugf("checking new content %v:%v", keyNode.Value, valueEl.Value.(*yaml.Node).Value)
+		if keyNode.Value == key.Value && keyNode.Alias == nil && key.Alias == nil {
+			log.Debugf("overridign new content")
+			valueEl.Value = value
+			return nil
+		}
+		newEl = valueEl // move forward twice
+	}
+
+	for index := startIndex + 2; index < len(node.Content); index = index + 2 {
+		keyNode := node.Content[index]
+
+		if keyNode.Value == key.Value && keyNode.Alias == nil {
+			log.Debugf("content will be overridden at index %v", index)
+			return nil
+		}
+	}
+
+	err = explodeNode(key, newContent)
+	if err != nil {
+		return err
+	}
+	log.Debugf("adding %v:%v", key.Value, value.Value)
+	newContent.MatchingNodes.PushBack(key)
+	newContent.MatchingNodes.PushBack(value)
+	return nil
+}

pkg/yqlib/operator_anchors_aliases_test.go

@@ -0,0 +1,207 @@
+package yqlib
+
+import (
+	"testing"
+)
+
+var specDocument = `- &CENTER { x: 1, y: 2 }
+- &LEFT { x: 0, y: 2 }
+- &BIG { r: 10 }
+- &SMALL { r: 1 }
+`
+
+var expectedSpecResult = "D0, P[4], (!!map)::x: 1\ny: 2\nr: 10\n"
+
+var anchorOperatorScenarios = []expressionScenario{
+	{
+		description:    "Merge one map",
+		subdescription: "see https://yaml.org/type/merge.html",
+		document:       specDocument + "- << : *CENTER\n  r: 10\n",
+		expression:     ".[4] | explode(.)",
+		expected:       []string{expectedSpecResult},
+	},
+	{
+		description:    "Merge multiple maps",
+		subdescription: "see https://yaml.org/type/merge.html",
+		document:       specDocument + "- << : [ *CENTER, *BIG ]\n",
+		expression:     ".[4] | explode(.)",
+		expected:       []string{"D0, P[4], (!!map)::r: 10\nx: 1\ny: 2\n"},
+	},
+	{
+		description:    "Override",
+		subdescription: "see https://yaml.org/type/merge.html",
+		document:       specDocument + "- << : [ *BIG, *LEFT, *SMALL ]\n  x: 1\n",
+		expression:     ".[4] | explode(.)",
+		expected:       []string{"D0, P[4], (!!map)::r: 10\nx: 1\ny: 2\n"},
+	},
+	{
+		description: "Get anchor",
+		document:    `a: &billyBob cat`,
+		expression:  `.a | anchor`,
+		expected: []string{
+			"D0, P[a], (!!str)::billyBob\n",
+		},
+	},
+	{
+		description: "Set anchor",
+		document:    `a: cat`,
+		expression:  `.a anchor = "foobar"`,
+		expected: []string{
+			"D0, P[], (doc)::a: &foobar cat\n",
+		},
+	},
+	{
+		description: "Set anchor relatively using assign-update",
+		document:    `a: {b: cat}`,
+		expression:  `.a anchor |= .b`,
+		expected: []string{
+			"D0, P[], (doc)::a: &cat {b: cat}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `a: {c: cat}`,
+		expression: `.a anchor |= .b`,
+		expected: []string{
+			"D0, P[], (doc)::a: {c: cat}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `a: {c: cat}`,
+		expression: `.a anchor = .b`,
+		expected: []string{
+			"D0, P[], (doc)::a: {c: cat}\n",
+		},
+	},
+	{
+		description: "Get alias",
+		document:    `{b: &billyBob meow, a: *billyBob}`,
+		expression:  `.a | alias`,
+		expected: []string{
+			"D0, P[a], (!!str)::billyBob\n",
+		},
+	},
+	{
+		description: "Set alias",
+		document:    `{b: &meow purr, a: cat}`,
+		expression:  `.a alias = "meow"`,
+		expected: []string{
+			"D0, P[], (doc)::{b: &meow purr, a: *meow}\n",
+		},
+	},
+	{
+		description: "Set alias to blank does nothing",
+		document:    `{b: &meow purr, a: cat}`,
+		expression:  `.a alias = ""`,
+		expected: []string{
+			"D0, P[], (doc)::{b: &meow purr, a: cat}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{b: &meow purr, a: cat}`,
+		expression: `.a alias = .c`,
+		expected: []string{
+			"D0, P[], (doc)::{b: &meow purr, a: cat}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{b: &meow purr, a: cat}`,
+		expression: `.a alias |= .c`,
+		expected: []string{
+			"D0, P[], (doc)::{b: &meow purr, a: cat}\n",
+		},
+	},
+	{
+		description: "Set alias relatively using assign-update",
+		document:    `{b: &meow purr, a: {f: meow}}`,
+		expression:  `.a alias |= .f`,
+		expected: []string{
+			"D0, P[], (doc)::{b: &meow purr, a: *meow}\n",
+		},
+	},
+	{
+		description: "Explode alias and anchor",
+		document:    `{f : {a: &a cat, b: *a}}`,
+		expression:  `explode(.f)`,
+		expected: []string{
+			"D0, P[], (doc)::{f: {a: cat, b: cat}}\n",
+		},
+	},
+	{
+		description: "Explode with no aliases or anchors",
+		document:    `a: mike`,
+		expression:  `explode(.a)`,
+		expected: []string{
+			"D0, P[], (doc)::a: mike\n",
+		},
+	},
+	{
+		description: "Explode with alias keys",
+		document:    `{f : {a: &a cat, *a: b}}`,
+		expression:  `explode(.f)`,
+		expected: []string{
+			"D0, P[], (doc)::{f: {a: cat, cat: b}}\n",
+		},
+	},
+	{
+		description: "Explode with merge anchors",
+		document:    mergeDocSample,
+		expression:  `explode(.)`,
+		expected: []string{`D0, P[], (doc)::foo:
+    a: foo_a
+    thing: foo_thing
+    c: foo_c
+bar:
+    b: bar_b
+    thing: bar_thing
+    c: bar_c
+foobarList:
+    b: bar_b
+    thing: foo_thing
+    c: foobarList_c
+    a: foo_a
+foobar:
+    c: foo_c
+    a: foo_a
+    thing: foobar_thing
+`},
+	},
+	{
+		skipDoc:    true,
+		document:   mergeDocSample,
+		expression: `.foo* | explode(.) | (. style="flow")`,
+		expected: []string{
+			"D0, P[foo], (!!map)::{a: foo_a, thing: foo_thing, c: foo_c}\n",
+			"D0, P[foobarList], (!!map)::{b: bar_b, thing: foo_thing, c: foobarList_c, a: foo_a}\n",
+			"D0, P[foobar], (!!map)::{c: foo_c, a: foo_a, thing: foobar_thing}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   mergeDocSample,
+		expression: `.foo* | explode(explode(.)) | (. style="flow")`,
+		expected: []string{
+			"D0, P[foo], (!!map)::{a: foo_a, thing: foo_thing, c: foo_c}\n",
+			"D0, P[foobarList], (!!map)::{b: bar_b, thing: foo_thing, c: foobarList_c, a: foo_a}\n",
+			"D0, P[foobar], (!!map)::{c: foo_c, a: foo_a, thing: foobar_thing}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{f : {a: &a cat, b: &b {f: *a}, *a: *b}}`,
+		expression: `explode(.f)`,
+		expected: []string{
+			"D0, P[], (doc)::{f: {a: cat, b: {f: cat}, cat: {f: cat}}}\n",
+		},
+	},
+}
+
+func TestAnchorAliasOperatorScenarios(t *testing.T) {
+	for _, tt := range anchorOperatorScenarios {
+		testScenario(t, &tt)
+	}
+	documentScenarios(t, "Anchor and Alias Operators", anchorOperatorScenarios)
+}

pkg/yqlib/operator_assign.go

@@ -1,70 +1,61 @@
 package yqlib
 
-import "container/list"
-
-type AssignOpPreferences struct {
-	UpdateAssign bool
-}
-
-func AssignUpdateOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
+func assignUpdateOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-	preferences := pathNode.Operation.Preferences.(*AssignOpPreferences)
-
-	var rhs *list.List
-	if !preferences.UpdateAssign {
-		rhs, err = d.GetMatchingNodes(matchingNodes, pathNode.Rhs)
+	var rhs Context
+	if !expressionNode.Operation.UpdateAssign {
+		rhs, err = d.GetMatchingNodes(context.ReadOnlyClone(), expressionNode.Rhs)
 	}
 
-	for el := lhs.Front(); el != nil; el = el.Next() {
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 
-		if preferences.UpdateAssign {
-			rhs, err = d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		if expressionNode.Operation.UpdateAssign {
+			rhs, err = d.GetMatchingNodes(context.SingleChildContext(candidate), expressionNode.Rhs)
 		}
 
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
 		// grab the first value
-		first := rhs.Front()
+		first := rhs.MatchingNodes.Front()
 
 		if first != nil {
-			candidate.UpdateFrom(first.Value.(*CandidateNode))
+			rhsCandidate := first.Value.(*CandidateNode)
+			rhsCandidate.Node = unwrapDoc(rhsCandidate.Node)
+			candidate.UpdateFrom(rhsCandidate)
 		}
 	}
-	// // if there was nothing given, perhaps we are creating a new yaml doc
-	// if matchingNodes.Len() == 0 {
-	// 	log.Debug("started with nothing, returning LHS, %v", lhs.Len())
-	// 	return lhs, nil
-	// }
-	return matchingNodes, nil
+
+	return context, nil
 }
 
 // does not update content or values
-func AssignAttributesOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
-	lhs, err := d.GetMatchingNodes(matchingNodes, pathNode.Lhs)
+func assignAttributesOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	log.Debug("getting lhs matching nodes for update")
+	lhs, err := d.GetMatchingNodes(context, expressionNode.Lhs)
 	if err != nil {
-		return nil, err
+		return Context{}, err
 	}
-	for el := lhs.Front(); el != nil; el = el.Next() {
+	for el := lhs.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 
-		rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		rhs, err := d.GetMatchingNodes(context.SingleReadonlyChildContext(candidate), expressionNode.Rhs)
 
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
 
 		// grab the first value
-		first := rhs.Front()
+		first := rhs.MatchingNodes.Front()
 
 		if first != nil {
 			candidate.UpdateAttributesFrom(first.Value.(*CandidateNode))
 		}
 	}
-	return matchingNodes, nil
+	return context, nil
 }

pkg/yqlib/operator_assign_test.go

@@ -12,6 +12,22 @@ var assignOperatorScenarios = []expressionScenario{
 			"D0, P[], ()::a:\n    b: cat\nx: frog\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		document:   "{}",
+		expression: `.a |= .b`,
+		expected: []string{
+			"D0, P[], (doc)::{a: null}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   "{}",
+		expression: `.a = .b`,
+		expected: []string{
+			"D0, P[], (doc)::{a: null}\n",
+		},
+	},
 	{
 		description: "Update node to be the child value",
 		document:    `{a: {b: {g: foof}}}`,
@@ -20,6 +36,16 @@ var assignOperatorScenarios = []expressionScenario{
 			"D0, P[], (doc)::{a: {g: foof}}\n",
 		},
 	},
+	{
+		description:    "Update node from another file",
+		subdescription: "Note this will also work when the second file is a scalar (string/number)",
+		document:       `{a: apples}`,
+		document2:      "{b: bob}",
+		expression:     `select(fileIndex==0).a = select(fileIndex==1) | select(fileIndex==0)`,
+		expected: []string{
+			"D0, P[], (doc)::{a: {b: bob}}\n",
+		},
+	},
 	{
 		description: "Update node to be the sibling value",
 		document:    `{a: {b: child}, b: sibling}`,
@@ -80,7 +106,15 @@ var assignOperatorScenarios = []expressionScenario{
 	{
 		description: "Update selected results",
 		document:    `{a: {b: apple, c: cactus}}`,
-		expression:  `(.a.[] | select(. == "apple")) = "frog"`,
+		expression:  `(.a[] | select(. == "apple")) = "frog"`,
+		expected: []string{
+			"D0, P[], (doc)::{a: {b: frog, c: cactus}}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{a: {b: apple, c: cactus}}`,
+		expression: `(.a.[] | select(. == "apple")) = "frog"`,
 		expected: []string{
 			"D0, P[], (doc)::{a: {b: frog, c: cactus}}\n",
 		},
@@ -125,5 +159,5 @@ func TestAssignOperatorScenarios(t *testing.T) {
 	for _, tt := range assignOperatorScenarios {
 		testScenario(t, &tt)
 	}
-	documentScenarios(t, "Assign", assignOperatorScenarios)
+	documentScenarios(t, "Assign (Update)", assignOperatorScenarios)
 }

pkg/yqlib/operator_booleans.go

@@ -2,14 +2,13 @@ package yqlib
 
 import (
 	"container/list"
+	"fmt"
 
 	yaml "gopkg.in/yaml.v3"
 )
 
-func isTruthy(c *CandidateNode) (bool, error) {
-	node := UnwrapDoc(c.Node)
+func isTruthyNode(node *yaml.Node) (bool, error) {
 	value := true
-
 	if node.Tag == "!!null" {
 		return false, nil
 	}
@@ -23,91 +22,146 @@ func isTruthy(c *CandidateNode) (bool, error) {
 	return value, nil
 }
 
+func isTruthy(c *CandidateNode) (bool, error) {
+	node := unwrapDoc(c.Node)
+	return isTruthyNode(node)
+}
+
 type boolOp func(bool, bool) bool
 
-func performBoolOp(results *list.List, lhs *list.List, rhs *list.List, op boolOp) error {
-	for lhsChild := lhs.Front(); lhsChild != nil; lhsChild = lhsChild.Next() {
-		lhsCandidate := lhsChild.Value.(*CandidateNode)
-		lhsTrue, errDecoding := isTruthy(lhsCandidate)
-		if errDecoding != nil {
-			return errDecoding
+func performBoolOp(op boolOp) func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+	return func(d *dataTreeNavigator, context Context, lhs *CandidateNode, rhs *CandidateNode) (*CandidateNode, error) {
+		owner := lhs
+
+		if lhs == nil && rhs == nil {
+			owner = &CandidateNode{}
+		} else if lhs == nil {
+			owner = rhs
 		}
 
-		for rhsChild := rhs.Front(); rhsChild != nil; rhsChild = rhsChild.Next() {
-			rhsCandidate := rhsChild.Value.(*CandidateNode)
-			rhsTrue, errDecoding := isTruthy(rhsCandidate)
+		var errDecoding error
+		lhsTrue := false
+		if lhs != nil {
+			lhs.Node = unwrapDoc(lhs.Node)
+			lhsTrue, errDecoding = isTruthy(lhs)
+
 			if errDecoding != nil {
-				return errDecoding
+				return nil, errDecoding
 			}
-			boolResult := createBooleanCandidate(lhsCandidate, op(lhsTrue, rhsTrue))
-			results.PushBack(boolResult)
 		}
+		log.Debugf("-- lhsTrue", lhsTrue)
+
+		rhsTrue := false
+		if rhs != nil {
+			rhs.Node = unwrapDoc(rhs.Node)
+			rhsTrue, errDecoding = isTruthy(rhs)
+			if errDecoding != nil {
+				return nil, errDecoding
+			}
+		}
+		log.Debugf("-- rhsTrue", rhsTrue)
+
+		return createBooleanCandidate(owner, op(lhsTrue, rhsTrue)), nil
 	}
-	return nil
 }
 
-func booleanOp(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode, op boolOp) (*list.List, error) {
+func findBoolean(wantBool bool, d *dataTreeNavigator, context Context, expressionNode *ExpressionNode, sequenceNode *yaml.Node) (bool, error) {
+	for _, node := range sequenceNode.Content {
+
+		if expressionNode != nil {
+			//need to evaluate the expression against the node
+			candidate := &CandidateNode{Node: node}
+			rhs, err := d.GetMatchingNodes(context.SingleReadonlyChildContext(candidate), expressionNode)
+			if err != nil {
+				return false, err
+			}
+			if rhs.MatchingNodes.Len() > 0 {
+				node = rhs.MatchingNodes.Front().Value.(*CandidateNode).Node
+			} else {
+				// no results found, ignore this entry
+				continue
+			}
+		}
+
+		truthy, err := isTruthyNode(node)
+		if err != nil {
+			return false, err
+		}
+		if truthy == wantBool {
+			return true, nil
+		}
+	}
+	return false, nil
+}
+
+func allOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	var results = list.New()
 
-	if matchingNodes.Len() == 0 {
-		lhs, err := d.GetMatchingNodes(list.New(), pathNode.Lhs)
-		if err != nil {
-			return nil, err
-		}
-		rhs, err := d.GetMatchingNodes(list.New(), pathNode.Rhs)
-		if err != nil {
-			return nil, err
-		}
-		return results, performBoolOp(results, lhs, rhs, op)
-	}
-
-	for el := matchingNodes.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
-		lhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Lhs)
-		if err != nil {
-			return nil, err
+		candidateNode := unwrapDoc(candidate.Node)
+		if candidateNode.Kind != yaml.SequenceNode {
+			return Context{}, fmt.Errorf("any only supports arrays, was %v", candidateNode.Tag)
 		}
-		rhs, err := d.GetMatchingNodes(nodeToMap(candidate), pathNode.Rhs)
+		booleanResult, err := findBoolean(false, d, context, expressionNode.Rhs, candidateNode)
 		if err != nil {
-			return nil, err
+			return Context{}, err
 		}
-
-		err = performBoolOp(results, lhs, rhs, op)
-		if err != nil {
-			return nil, err
-		}
-
+		result := createBooleanCandidate(candidate, !booleanResult)
+		results.PushBack(result)
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }
 
-func OrOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func anyOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
+	var results = list.New()
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		candidateNode := unwrapDoc(candidate.Node)
+		if candidateNode.Kind != yaml.SequenceNode {
+			return Context{}, fmt.Errorf("any only supports arrays, was %v", candidateNode.Tag)
+		}
+		booleanResult, err := findBoolean(true, d, context, expressionNode.Rhs, candidateNode)
+		if err != nil {
+			return Context{}, err
+		}
+		result := createBooleanCandidate(candidate, booleanResult)
+		results.PushBack(result)
+	}
+	return context.ChildContext(results), nil
+}
+
+func orOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- orOp")
-	return booleanOp(d, matchingNodes, pathNode, func(b1 bool, b2 bool) bool {
-		return b1 || b2
-	})
+	return crossFunction(d, context.ReadOnlyClone(), expressionNode, performBoolOp(
+		func(b1 bool, b2 bool) bool {
+			log.Debugf("-- peformingOrOp with %v and %v", b1, b2)
+			return b1 || b2
+		}), true)
 }
 
-func AndOperator(d *dataTreeNavigator, matchingNodes *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func andOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- AndOp")
-	return booleanOp(d, matchingNodes, pathNode, func(b1 bool, b2 bool) bool {
-		return b1 && b2
-	})
+	return crossFunction(d, context.ReadOnlyClone(), expressionNode, performBoolOp(
+		func(b1 bool, b2 bool) bool {
+			return b1 && b2
+		}), true)
 }
 
-func NotOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func notOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- notOperation")
 	var results = list.New()
 
-	for el := matchMap.Front(); el != nil; el = el.Next() {
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
 		candidate := el.Value.(*CandidateNode)
 		log.Debug("notOperation checking %v", candidate)
 		truthy, errDecoding := isTruthy(candidate)
 		if errDecoding != nil {
-			return nil, errDecoding
+			return Context{}, errDecoding
 		}
 		result := createBooleanCandidate(candidate, !truthy)
 		results.PushBack(result)
 	}
-	return results, nil
+	return context.ChildContext(results), nil
 }

pkg/yqlib/operator_booleans_test.go

@@ -6,14 +6,38 @@ import (
 
 var booleanOperatorScenarios = []expressionScenario{
 	{
-		description: "OR example",
+		description: "`or` example",
 		expression:  `true or false`,
 		expected: []string{
 			"D0, P[], (!!bool)::true\n",
 		},
 	},
 	{
-		description: "AND example",
+		skipDoc:    true,
+		document:   "b: hi",
+		expression: `.a or .c`,
+		expected: []string{
+			"D0, P[], (!!bool)::false\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   "b: hi",
+		expression: `select(.a or .b)`,
+		expected: []string{
+			"D0, P[], (doc)::b: hi\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   "b: hi",
+		expression: `select((.a and .b) | not)`,
+		expected: []string{
+			"D0, P[], (doc)::b: hi\n",
+		},
+	},
+	{
+		description: "`and` example",
 		expression:  `true and false`,
 		expected: []string{
 			"D0, P[], (!!bool)::false\n",
@@ -27,6 +51,86 @@ var booleanOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!seq)::- {a: bird, b: dog}\n- {a: cat, b: fly}\n",
 		},
 	},
+	{
+		description: "`any` returns true if any boolean in a given array is true",
+		document:    `[false, true]`,
+		expression:  "any",
+		expected: []string{
+			"D0, P[], (!!bool)::true\n",
+		},
+	},
+	{
+		description: "`any` returns false for an empty array",
+		document:    `[]`,
+		expression:  "any",
+		expected: []string{
+			"D0, P[], (!!bool)::false\n",
+		},
+	},
+	{
+		description: "`any_c` returns true if any element in the array is true for the given condition.",
+		document:    "a: [rad, awesome]\nb: [meh, whatever]",
+		expression:  `.[] |= any_c(. == "awesome")`,
+		expected: []string{
+			"D0, P[], (doc)::a: true\nb: false\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `[{pet: cat}]`,
+		expression: `any_c(.name == "harry") as $c`,
+		expected: []string{
+			"D0, P[], (doc)::[{pet: cat}]\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `[{pet: cat}]`,
+		expression: `all_c(.name == "harry") as $c`,
+		expected: []string{
+			"D0, P[], (doc)::[{pet: cat}]\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `[false, false]`,
+		expression: "any",
+		expected: []string{
+			"D0, P[], (!!bool)::false\n",
+		},
+	},
+	{
+		description: "`all` returns true if all booleans in a given array are true",
+		document:    `[true, true]`,
+		expression:  "all",
+		expected: []string{
+			"D0, P[], (!!bool)::true\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `[false, true]`,
+		expression: "all",
+		expected: []string{
+			"D0, P[], (!!bool)::false\n",
+		},
+	},
+	{
+		description: "`all` returns true for an empty array",
+		document:    `[]`,
+		expression:  "all",
+		expected: []string{
+			"D0, P[], (!!bool)::true\n",
+		},
+	},
+	{
+		description: "`all_c` returns true if all elements in the array are true for the given condition.",
+		document:    "a: [rad, awesome]\nb: [meh, 12]",
+		expression:  `.[] |= all_c(tag == "!!str")`,
+		expected: []string{
+			"D0, P[], (doc)::a: true\nb: false\n",
+		},
+	},
 	{
 		skipDoc:    true,
 		expression: `false or false`,
@@ -45,6 +149,22 @@ var booleanOperatorScenarios = []expressionScenario{
 			"D0, P[b], (!!bool)::true\n",
 		},
 	},
+	{
+		skipDoc:    true,
+		document:   `{}`,
+		expression: `(.a.b or .c) as $x`,
+		expected: []string{
+			"D0, P[], (doc)::{}\n",
+		},
+	},
+	{
+		skipDoc:    true,
+		document:   `{}`,
+		expression: `(.a.b and .c) as $x`,
+		expected: []string{
+			"D0, P[], (doc)::{}\n",
+		},
+	},
 	{
 		description: "Not true is false",
 		expression:  `true | not`,

pkg/yqlib/operator_collect.go

@@ -6,34 +6,35 @@ import (
 	yaml "gopkg.in/yaml.v3"
 )
 
-func CollectOperator(d *dataTreeNavigator, matchMap *list.List, pathNode *PathTreeNode) (*list.List, error) {
+func collectOperator(d *dataTreeNavigator, context Context, expressionNode *ExpressionNode) (Context, error) {
 	log.Debugf("-- collectOperation")
 
-	if matchMap.Len() == 0 {
+	if context.MatchingNodes.Len() == 0 {
 		node := &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq", Value: "[]"}
 		candidate := &CandidateNode{Node: node}
-		return nodeToMap(candidate), nil
+		return context.SingleChildContext(candidate), nil
 	}
 
 	var results = list.New()
 
 	node := &yaml.Node{Kind: yaml.SequenceNode, Tag: "!!seq"}
-
-	var document uint = 0
-	var path []interface{}
-
-	for el := matchMap.Front(); el != nil; el = el.Next() {
-		candidate := el.Value.(*CandidateNode)
-		log.Debugf("Collecting %v", NodeToString(candidate))
-		if path == nil && candidate.Path != nil && len(candidate.Path) > 1 {
-			path = candidate.Path[:len(candidate.Path)-1]
-			document = candidate.Document
+	var collectC *CandidateNode
+	if context.MatchingNodes.Front() != nil {
+		collectC = context.MatchingNodes.Front().Value.(*CandidateNode).CreateChild(nil, node)
+		if len(collectC.Path) > 0 {
+			collectC.Path = collectC.Path[:len(collectC.Path)-1]
 		}
-		node.Content = append(node.Content, candidate.Node)
+	} else {
+		collectC = &CandidateNode{Node: node}
+	}
+
+	for el := context.MatchingNodes.Front(); el != nil; el = el.Next() {
+		candidate := el.Value.(*CandidateNode)
+		log.Debugf("Collecting %v", NodeToString(candidate))
+		node.Content = append(node.Content, unwrapDoc(candidate.Node))
 	}
 
-	collectC := &CandidateNode{Node: node, Document: document, Path: path}
 	results.PushBack(collectC)
 
-	return results, nil
+	return context.ChildContext(results), nil
 }