String Operators

RegEx
This uses Golang's native regex functions under the hood - See their docs for the supported syntax.
Case insensitive tip: prefix the regex with (?i) - e.g. test("(?i)cats)".
match(regEx)
This operator returns the substring match details of the given regEx.
capture(regEx)
Capture returns named RegEx capture groups in a map. Can be more convenient than match depending on what you are doing.
test(regEx)
Returns true if the string matches the RegEx, false otherwise.
sub(regEx, replacement)
Substitutes matched substrings. The first parameter is the regEx to match substrings within the original string. The second parameter specifies what to replace those matches with. This can refer to capture groups from the first RegEx.
String blocks, bash and newlines
Bash is notorious for chomping on precious trailing newline characters, making it tricky to set strings with newlines properly. In particular, the $( exp ) will trim trailing newlines.
For instance to get this yaml:
a: |
  cat
Using $( exp ) wont work, as it will trim the trailing newline.
m=$(echo "cat\n") yq -n '.a = strenv(m)'
a: cat
However, using printf works:
printf -v m "cat\n" ; m="$m" yq -n '.a = strenv(m)'
a: |
  cat
As well as having multiline expressions:
m="cat
"  yq -n '.a = strenv(m)'
a: |
  cat
Similarly, if you're trying to set the content from a file, and want a trailing newline:
IFS= read -rd '' output < <(cat my_file)
output=$output ./yq '.data.values = strenv(output)' first.yml
To up (upper) case
Works with unicode characters
Given a sample.yml file of:
água
then
yq 'upcase' sample.yml
will output
ÁGUA
To down (lower) case
Works with unicode characters
Given a sample.yml file of:
ÁgUA
then
yq 'downcase' sample.yml
will output
água
Join strings
Given a sample.yml file of:
- cat
- meow
- 1
- null
- true
then
yq 'join("; ")' sample.yml
will output
cat; meow; 1; ; true
Trim strings
Given a sample.yml file of:
- ' cat'
- 'dog '
- ' cow cow '
- horse
then
yq '.[] | trim' sample.yml
will output
cat
dog
cow cow
horse
Match string
Given a sample.yml file of:
foo bar foo
then
yq 'match("foo")' sample.yml
will output
string: foo
offset: 0
length: 3
captures: []
Match string, case insensitive
Given a sample.yml file of:
foo bar FOO
then
yq '[match("(?i)foo"; "g")]' sample.yml
will output
- string: foo
  offset: 0
  length: 3
  captures: []
- string: FOO
  offset: 8
  length: 3
  captures: []
Match with global capture group
Given a sample.yml file of:
abc abc
then
yq '[match("(ab)(c)"; "g")]' sample.yml
will output
- string: abc
  offset: 0
  length: 3
  captures:
    - string: ab
      offset: 0
      length: 2
    - string: c
      offset: 2
      length: 1
- string: abc
  offset: 4
  length: 3
  captures:
    - string: ab
      offset: 4
      length: 2
    - string: c
      offset: 6
      length: 1
Match with named capture groups
Given a sample.yml file of:
foo bar foo foo  foo
then
yq '[match("foo (?P<bar123>bar)? foo"; "g")]' sample.yml
will output
- string: foo bar foo
  offset: 0
  length: 11
  captures:
    - string: bar
      offset: 4
      length: 3
      name: bar123
- string: foo  foo
  offset: 12
  length: 8
  captures:
    - string: null
      offset: -1
      length: 0
      name: bar123
Capture named groups into a map
Given a sample.yml file of:
xyzzy-14
then
yq 'capture("(?P<a>[a-z]+)-(?P<n>[0-9]+)")' sample.yml
will output
a: xyzzy
n: "14"
Match without global flag
Given a sample.yml file of:
cat cat
then
yq 'match("cat")' sample.yml
will output
string: cat
offset: 0
length: 3
captures: []
Match with global flag
Given a sample.yml file of:
cat cat
then
yq '[match("cat"; "g")]' sample.yml
will output
- string: cat
  offset: 0
  length: 3
  captures: []
- string: cat
  offset: 4
  length: 3
  captures: []
Test using regex
Like jq's equivalent, this works like match but only returns true/false instead of full match details
Given a sample.yml file of:
- cat
- dog
then
yq '.[] | test("at")' sample.yml
will output
true
false
Substitute / Replace string
This uses Golang's regex, described here. Note the use of |= to run in context of the current string value.
Given a sample.yml file of:
a: dogs are great
then
yq '.a |= sub("dogs", "cats")' sample.yml
will output
a: cats are great
Substitute / Replace string with regex
This uses Golang's regex, described here. Note the use of |= to run in context of the current string value.
Given a sample.yml file of:
a: cat
b: heat
then
yq '.[] |= sub("(a)", "${1}r")' sample.yml
will output
a: cart
b: heart
Custom types: that are really strings
When custom tags are encountered, yq will try to decode the underlying type.
Given a sample.yml file of:
a: !horse cat
b: !goat heat
then
yq '.[] |= sub("(a)", "${1}r")' sample.yml
will output
a: !horse cart
b: !goat heart
Split strings
Given a sample.yml file of:
cat; meow; 1; ; true
then
yq 'split("; ")' sample.yml
will output
- cat
- meow
- "1"
- ""
- "true"
Split strings one match
Given a sample.yml file of:
word
then
yq 'split("; ")' sample.yml
will output
- word
Split into Documents
Style
Last modified 6mo ago