yq/pkg/yqlib/doc/operators/headers/string-operators.md

String Operators

RegEx

This uses golangs native regex functions under the hood - See https://github.com/google/re2/wiki/Syntax for the supported syntax.

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 new line.

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 new line:

IFS= read -rd '' output < <(cat my_file)
output=$output ./yq '.data.values = strenv(output)' first.yml