On publish or publish-on-error in Mistral workflow, YAQL or Jinja expressions can be used. There is a regex_match, regex_replace, regex_search, and regex_substring custom functions/filters that StackStorm include. The following is an example in YAQL using regex_match. More examples can be found at st2/contrib/examples/actions/workflows/tests at master · StackStorm/st2 · GitHub.
version: '2.0'
examples.mistral-test-func-regex-match:
description: A workflow for testing regex_match custom filter in mistral
type: direct
input:
- input_str
- regex_pattern
output:
result_jinja: <% $.result_jinja %>
result_yaql: <% $.result_yaql %>
tasks:
task1:
action: std.noop
publish:
result_jinja: '{{ regex_match(_.input_str, _.regex_pattern) }}'
result_yaql: '<% regex_match($.input_str, $.regex_pattern) %>'