Gitlab CI - Custom variable as a branch in trigger downstream

Question

I would like to use a custom variable as branch inside a trigger downstream stage, but it looks like so far that before_script (when I put the variable assignment) is not called before a trigger stage. That leads to not have the desired branch triggered, because of empty $CUSTOM_VARIABLE.

Basically, this is to trigger the child on a specific TAG name instead of the branch name, if TAG is given...

Here is a sample code showing what I want to do:

default:
  before_script:
      if [ $CONDITION ];
      then
         CUSTOM_VARIABLE=$TAG_NAME;
      else
         CUSTOM_VARIABLE=$CI_COMMIT_REF_NAME;
      fi

build:
  stage: build
  variables:
    VAR1: var1
    VAR2: var2
  trigger:
    project: my/child/project
    branch: $CUSTOM_VARIABLE
    strategy: depend

I also tried to assign the variable conditionally inside variables, but the code is not evaluated and is pasted as it is inside the custom variable.

variables:
  CUSTOM_VARIABLE: $([ $CONDITION ] && echo "$TAG_NAME" || echo "$CI_COMMIT_REF_NAME")

Is there a way to use a custom variable as a trigger branch ?

Answer 1

You need to use dotenv

before_script:
      if [ $CONDITION ];
      then
         CUSTOM_VARIABLE=$TAG_NAME;
         echo "CUSTOM_VARIABLE=$CUSTOM_VARIABLE" >> build.env
      else
         CUSTOM_VARIABLE=$CI_COMMIT_REF_NAME;
         echo "CUSTOM_VARIABLE=$CUSTOM_VARIABLE" >> build.env
      fi
artifacts:
    reports:
      dotenv: build.env