Why doesn't nested parameter expansion work correctly in GitLab CI/CD?

Question

Using a bash runner, is there any reason why the following variable expansion shouldn't work?

variables:
  GIT_BRANCH: "${CI_MERGE_REQUEST_SOURCE_BRANCH_NAME:-${CI_COMMIT_BRANCH:-$CI_DEFAULT_BRANCH}}"

job1:
  script:
    - echo $GIT_BRANCH

The job outputs }.

I'm using GitLab Enterprise Edition 14.1.8-ee.

John Kugelman · Accepted Answer · 2022-02-08T17:42:33.987

3

These expansions are done by GitLab CI, not by bash, so they probably simply can't handle nested expansions as robustly as bash can.

They probably think the variable name is everything up to the next }, so CI_MERGE_REQUEST_SOURCE_BRANCH_NAME:-${CI_COMMIT_BRANCH:-$CI_DEFAULT_BRANCH without a closing curly brace. That would explain why there is a leftover } when the dust settles.

edited Feb 08 '22 at 17:42

answered Feb 08 '22 at 17:33

John Kugelman

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Tolis Gerodimos · Answer 2 · 2022-02-08T20:29:05.160

2

Gitlab variables can not perform bash operations as you try here.

Gitlab understands ${VARIABLE_NAME}

In your case

${CI_MERGE_REQUEST_SOURCE_BRANCH_NAME:-${CI_COMMIT_BRANCH:-$CI_DEFAULT_BRANCH}}

Gitlab tries to find the variable CI_MERGE_REQUEST_SOURCE_BRANCH_NAME:-${CI_COMMIT_BRANCH:-$CI_DEFAULT_BRANCH}

But this variable doesn't exist, so it only outputs }

edited Feb 08 '22 at 20:29

answered Feb 08 '22 at 17:33

Tolis Gerodimos

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score 1 · Answer 3 · answered Feb 08 '22 at 20:11

As stated by the other answers, this syntax won't expand how you expect. As a workaround, you might be able to use rules:variables: to get the same effect.

my_job:
  rules:
    - if: '$CI_MERGE_REQUEST_SOURCE_BRANCH_NAME'
      variables:
        GIT_BRANCH: $CI_MERGE_REQUEST_SOURCE_BRANCH_NAME
    - if: '$CI_COMMIT_BRANCH'
      variables:
        GIT_BRANCH: $CI_COMMIT_BRANCH
    - when: on_success
  variables:
    GIT_BRANCH: $CI_DEFAULT_BRANCH

You could also consider simply setting the variable directly in the job script using export. Then the bash variable expansion will work as expected.

Why doesn't nested parameter expansion work correctly in GitLab CI/CD?

3 Answers3