yq/pkg/yqlib/doc/operators/comment-operators.md

Comment Operators

Use these comment operators to set or retrieve comments. Note that line comments on maps/arrays are actually set on the key node as opposed to the value (map/array). See below for examples.

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.

{% hint style="warning" %} Note that versions prior to 4.18 require the 'eval/e' command to be specified.

yq e <exp> <file> {% endhint %}

Set line comment

Set the comment on the key node for more reliability (see below).

Given a sample.yml file of:

a: cat

then

yq '.a line_comment="single"' sample.yml

will output

a: cat # single

Set line comment of a maps/arrays

For maps and arrays, you need to set the line comment on the key node. This will also work for scalars.

Given a sample.yml file of:

a:
  b: things

then

yq '(.a | key) line_comment="single"' sample.yml

will output

a: # single
  b: things

Use update assign to perform relative updates

Given a sample.yml file of:

a: cat
b: dog

then

yq '.. line_comment |= .' sample.yml

will output

a: cat # cat
b: dog # dog

Where is the comment - map key example

The underlying yaml parser can assign comments in a document to surprising nodes. Use an expression like this to find where you comment is. 'p' indicates the path, 'isKey' is if the node is a map key (as opposed to a map value). From this, you can see the 'hello-world-comment' is actually on the 'hello' key

Given a sample.yml file of:

hello: # hello-world-comment
  message: world

then

yq '[... | {"p": path | join("."), "isKey": is_key, "hc": headComment, "lc": lineComment, "fc": footComment}]' sample.yml

will output

- p: ""
  isKey: false
  hc: ""
  lc: ""
  fc: ""
- p: hello
  isKey: true
  hc: ""
  lc: hello-world-comment
  fc: ""
- p: hello
  isKey: false
  hc: ""
  lc: ""
  fc: ""
- p: hello.message
  isKey: true
  hc: ""
  lc: ""
  fc: ""
- p: hello.message
  isKey: false
  hc: ""
  lc: ""
  fc: ""

Retrieve comment - map key example

From the previous example, we know that the comment is on the 'hello' key as a lineComment

Given a sample.yml file of:

hello: # hello-world-comment
  message: world

then

yq '.hello | key | line_comment' sample.yml

will output

hello-world-comment

Where is the comment - array example

The underlying yaml parser can assign comments in a document to surprising nodes. Use an expression like this to find where you comment is. 'p' indicates the path, 'isKey' is if the node is a map key (as opposed to a map value). From this, you can see the 'under-name-comment' is actually on the first child

Given a sample.yml file of:

name:
  # under-name-comment
  - first-array-child

then

yq '[... | {"p": path | join("."), "isKey": is_key, "hc": headComment, "lc": lineComment, "fc": footComment}]' sample.yml

will output

- p: ""
  isKey: false
  hc: ""
  lc: ""
  fc: ""
- p: name
  isKey: true
  hc: ""
  lc: ""
  fc: ""
- p: name
  isKey: false
  hc: ""
  lc: ""
  fc: ""
- p: name.0
  isKey: false
  hc: under-name-comment
  lc: ""
  fc: ""

Retrieve comment - array example

From the previous example, we know that the comment is on the first child as a headComment

Given a sample.yml file of:

name:
  # under-name-comment
  - first-array-child

then

yq '.name[0] | headComment' sample.yml

will output

under-name-comment

Set head comment

Given a sample.yml file of:

a: cat

then

yq '. head_comment="single"' sample.yml

will output

# single

a: cat

Set head comment of a map entry

Given a sample.yml file of:

f: foo
a:
  b: cat

then

yq '(.a | key) head_comment="single"' sample.yml

will output

f: foo
# single
a:
  b: cat

Set foot comment, using an expression

Given a sample.yml file of:

a: cat

then

yq '. foot_comment=.a' sample.yml

will output

a: cat
# cat

Remove comment

Given a sample.yml file of:

a: cat # comment
b: dog # leave this

then

yq '.a line_comment=""' sample.yml

will output

a: cat
b: dog # leave this

Remove (strip) all comments

Note the use of ... to ensure key nodes are included.

Given a sample.yml file of:

a: cat # comment
# great
b: # key comment

then

yq '... comments=""' sample.yml

will output

a: cat
b:

Get line comment

Given a sample.yml file of:

a: cat # meow
# have a great day

then

yq '.a | line_comment' sample.yml

will output

meow

Get head comment

Given a sample.yml file of:

# welcome!

a: cat # meow

# have a great day

then

yq '. | head_comment' sample.yml

will output

welcome!

Head comment with document split

Given a sample.yml file of:

# welcome!
---
# bob
a: cat # meow

# have a great day

then

yq 'head_comment' sample.yml

will output

welcome!
bob

Get foot comment

Given a sample.yml file of:

# welcome!

a: cat # meow

# have a great day
# no really

then

yq '. | foot_comment' sample.yml

will output

have a great day
no really