AWS CodeBuild, buildspec.yml "bad substitution" error

user_1233305 0
Viewed 610

I'm using AWS CodeBuild, and I need to manipulate an environment variable. I originally tried using a bash pattern substitution, like this, in the buildspec.yml:

  build:
    on-failure: ABORT
    commands:
      - env="${CODEBUILD_WEBHOOK_TRIGGER/tag\//}"

CODEBUILD_WEBHOOK_TRIGGER should be something like tag/my-tag-name, and I want to remove the tag/ part of it. This command works fine from a local bash shell, but when performned in CodeBuild, this is the output:

[Container] 2021/08/02 21:29:28 Running command env="${CODEBUILD_WEBHOOK_TRIGGER/tag\//}"
/codebuild/output/tmp/script.sh: 4: Bad substitution
...
[Container] 2021/08/02 21:29:28 Phase context status code: COMMAND_EXECUTION_ERROR Message: Error while executing command: env="${CODEBUILD_WEBHOOK_TRIGGER/tag\//}". Reason: exit status 2

I ended up replacing the pattern substitution with an awk command just to get it working, but it makes for more complex code. And I don't understand why the pattern substitution doesn't work?

Here's the awk command I ended up using, which is working fine:

  build:
    on-failure: ABORT
    commands:
      - env="`echo $CODEBUILD_WEBHOOK_TRIGGER | awk -F/ '$1=="tag" {print $2;}'`"
aws-codebuild bash
2 Answers

CodeBuild might not be using bash. Try this :

env="${CODEBUILD_WEBHOOK_TRIGGER#tag/}"
user_21256710

Gordon's comment on the original post above explains why this happens - that bash extensions won't work on more basic shells (and it appears that CodeBuild's Ubuntu containers may use dash).

However, you can force CodeBuild to use bash with the following in your buildspec:

env:
  shell: bash

(documentation at https://docs.aws.amazon.com/codebuild/latest/userguide/build-spec-ref.html#build-spec-ref-syntax)

This should then allow you to use any of the substitutions supported by bash, and it appears to resolve this issue.

(Alternatively, if you're calling a separate shell script from your buildspec, you can just ensure that you have a shebang at the top of it).

user_19821360
Related