Add operator!

pkg/yqlib/doc/Add.md

@@ -0,0 +1,107 @@
+Add behaves differently according to the type of the LHS:
+- arrays: concatenate
+- number scalars: arithmetic addition (soon)
+- string scalars: concatenate (soon)
+## Concatenate arrays
+Given a sample.yml file of:
+```yaml
+a:
+  - 1
+  - 2
+b:
+  - 3
+  - 4
+```
+then
+```bash
+yq eval '.a + .b' sample.yml
+```
+will output
+```yaml
+- 1
+- 2
+- 3
+- 4
+```
+
+## Concatenate null to array
+Given a sample.yml file of:
+```yaml
+a:
+  - 1
+  - 2
+```
+then
+```bash
+yq eval '.a + null' sample.yml
+```
+will output
+```yaml
+- 1
+- 2
+```
+
+## Add object to array
+Given a sample.yml file of:
+```yaml
+a:
+  - 1
+  - 2
+c:
+  cat: meow
+```
+then
+```bash
+yq eval '.a + .c' sample.yml
+```
+will output
+```yaml
+- 1
+- 2
+- cat: meow
+```
+
+## Add string to array
+Given a sample.yml file of:
+```yaml
+a:
+  - 1
+  - 2
+```
+then
+```bash
+yq eval '.a + "hello"' sample.yml
+```
+will output
+```yaml
+- 1
+- 2
+- hello
+```
+
+## Update array (append)
+Given a sample.yml file of:
+```yaml
+a:
+  - 1
+  - 2
+b:
+  - 3
+  - 4
+```
+then
+```bash
+yq eval '.a = .a + .b' sample.yml
+```
+will output
+```yaml
+a:
+  - 1
+  - 2
+  - 3
+  - 4
+b:
+  - 3
+  - 4
+```
+

pkg/yqlib/doc/headers/Add.md

@@ -0,0 +1,4 @@
+Add behaves differently according to the type of the LHS:
+- arrays: concatenate
+- number scalars: arithmetic addition (soon)
+- string scalars: concatenate (soon)