yq/usage/path-expressions.md

description

description
Path expressions are used to deeply navigate and match particular yaml nodes.

Path Expressions

As a general rule, you should wrap paths in quotes to prevent your CLI from processing *, [] and other special characters.

Simple expressions

Maps

'a.b.c'

a:
  b:
    c: thing # MATCHES

Arrays

'a.b[1].c'

a:
  b:
  - c: thing0 
  - c: thing1 # MATCHES
  - c: thing2

Appending to arrays

e.g. when using the write command

'a.b[+].c'

a:
  b:
  - c: thing0

Will add a new entry:

a:
  b:
  - c: thing0 
  - c: thing1 # NEW entry from [+] on B array.

Negative Array indexes

Negative array indexes can be used to traverse the array in reverse

'a.b[-1].c'

Will access the last element in the b array and yield:

thing2

Splat

Maps

'a.*.c'

a:
  b1:
    c: thing # MATCHES
    d: whatever
  b2:
    c: thing # MATCHES
    f: something irrelevant

Prefix splat

'bob.item*.cats'

bob:
  item:
    cats: bananas # MATCHES
  something:
    cats: lemons
  itemThing:
    cats: more bananas # MATCHES
  item2:
    cats: apples # MATCHES
  thing:
    cats: oranges

Arrays

'a.b[*].c'

a:
  b:
  - c: thing0 # MATCHES
    d: what..ever
  - c: thing1 # MATCHES
    d: blarh
  - c: thing2 # MATCHES
    f: thingamabob

Deep Splat

** will match arbitrary nodes for both maps and arrays:

'a.**.c'

a:
  b1:
    c: thing1 # MATCHES
    d: cat cat
  b2:
    c: thing2 # MATCHES
    d: dog dog
  b3:
    d:
    - f:
        c: thing3 # MATCHES
        d: beep
    - f:
        g:
          c: thing4 # MATCHES
          d: boop
    - d: mooo

Search by children nodes

You can search children by nodes - note that this will return the parent of the matching expression, in the example below the parent(s) will be the matching indices of the 'a' array. We can then navigate down to get 'b.c' of each matching indice.

'a.(b.d==cat).b.c'

a:
  - b:
      c: thing0
      d: leopard
    ba: fast
  - b:
      c: thing1 # MATCHES
      d: cat
    ba: meowy
  - b:
      c: thing2
      d: caterpillar
    ba: icky
  - b:
      c: thing3 # MATCHES
      d: cat
    ba: also meowy

With prefixes

'a.(b.d==cat*).c'

a:
  - b:
      c: thing0
      d: leopard
    ba: fast
  - b:
      c: thing1 # MATCHES
      d: cat
    ba: meowy
  - b:
      c: thing2 # MATCHES
      d: caterpillar
    ba: icky
  - b:
      c: thing3 # MATCHES
      d: cat
    ba: also meowy

Matching children values

'animals(.==cat)'

animals:
  - dog
  - cat # MATCHES  
  - rat

this also works in maps, and with prefixes

'animals(.==c*)'

animals:
  friendliest: cow # MATCHES
  favourite: cat # MATCHES
  smallest: rat

Special Characters

When your yaml field has special characters that overlap with yq path expression characters, you will need to escape them in order for the command to work.

Keys with dots

When specifying a key that has a dot use key lookup indicator.

b:
  foo.bar: 7

yaml r sample.yaml 'b."foo.bar"'

yaml w sample.yaml 'b."foo.bar"' 9

Any valid yaml key can be specified as part of a key lookup.

Note that the path is in single quotes to avoid the double quotes being interpreted by your shell.

Keys and values with leading dashes

The flag terminator needs to be used to stop the app from attempting to parse the subsequent arguments as flags, if they start if a dash.

yq n -j -- --key --value

Will result in

--key: --value