Docker pre_build hook not matching $SOURCE_BRANCH names

Docker Hub
1

Hello, I’m trying to set up my pre_build hook in Docker so that if a build is triggered by a release branch, certain dependencies are updated. Our release branches follow a pretty standard release/<release_name> pattern, however the following conditional is not being triggered by our release branches:

if [[ "$SOURCE_BRANCH" = "develop" ]]; then
do something
elif [[ "$SOURCE_BRANCH" == "release/.*" ]]; then
do something
fi

Based on the sed commands I’ve used in Docker hooks previously, i’m not sure why this regex wouldn’t work. Any ideas?

2

I would be surprised if these regexp ever matched in if conditions.

Try it like this:

if [[ "${SOURCE_BRANCH}" == "develop" ]]; then 
  do something
elif [[ "${SOURCE_BRANCH}" =~ ^release/.*$ ]]; then
  do something else
fi
3

Thanks for the pointer, the second conditional worked. The check for develop has been working for a while now, is there a case in which it wouldn’t? And yeah I guess I’m not as familiar with this stuff as I’d thought. I tested on my machine by running echo release/<release name> | grep release/.*, and it matched the sample branch names. Any idea why it would work in a bash shell but not on Docker Hub?

4

That’s easy: the way you test for the condition is simply different. While you used grep’s pattern matching, the example I provided uses bash’s buildin regex matching for conditions.

This is not related to beeing executed in the bash shell or in a bash script, this is related to using the right "tool " for the right situation.

Create a bsh script with following content and save it as test.sh:

#!/bin/bash
if [[ "$SOURCE_BRANCH" == "develop" ]];then
  echo "develop: $SOURCE_BRANCH"
elif [[ "$SOURCE_BRANCH" =~ release/.* ]];then
  echo "release: $SOURCE_BRANCH"
fi

Then test it yourself:
test1: export SOURCE_BRANCH=develop && bash test.sh (I use bash to execute test.sh to skip “chmod +x test.sh”)
test2: export SOURCE_BRANCH=release/foo && bash test.sh

This approach does work on Dockerhub automated builds - I am using a similar snippets in pre_hooks myself.