How to change variable in gitlab cicd pipeline depending on branch - gitlab-ci

Question

I need to call a bash script from my gitlab cicd pipeline. When I call it, the input parameter needs to change depending on whether or not this is a merge into master. Basically what I want is this:
if master:
test:
stage: test
script:
- INPUT="foo"
- $(myscript.sh $INPUT)
if NOT master:
test:
stage: test
script:
- INPUT=""
- $(myscript.sh $INPUT)
I'm trying to figure out a way to set INPUT depending on which branch the pipeline is running on. I know there are rules as well as only/except, but they don't seem to allow you to set variable, only test them. I know the brute force way is to just write this twice, one with "only master" and another with "except master", but I would really like to avoid that.
Thanks

Answer 1

I implement this kind of thing using yml anchors to extend tasks.
I find it easier to read and customization can include other things, not only variables.
For example:
.test_my_software:
stage: test
script:
- echo ${MESSAGE}
- bash test.sh
test stable:
<<: *test_my_software
variables:
MESSAGE: testing stable code!
only:
- /stable.*/
test:
<<: *test_my_software
variables:
MESSAGE: testing our code!
except:
- /stable.*/
you get the idea...

Answer 2

Why not have two jobs to run the script and use rules to control when they are ran against master:
test:
stage: test
script:
- if [$CI_COMMIT_REF_NAME == 'master']; then export INPUT="foo"; else INPUT=""; fi
- $(myscript.sh $INPUT)