AWS Code Build: environment variables not found during CI jobs - amazon-web-services

Question

I usually name artifacts based on the commits they have been build from.
Based on this documentation, CODEBUILD_WEBHOOK_PREV_COMMIT is what I am looking for in AWS Code Build
Here is the buildspec.yml
phases:
install:
commands:
- apt-get update -y
build:
commands:
- export $CODEBUILD_WEBHOOK_PREV_COMMIT
- echo Entered the build phase...
- echo Build started on `date`
- mvn clean install -Dmaven.test.skip=true
- for f in ./target/*.car;do mv -- "$f" $(echo $f | sed -E "s/.car$/_${CODEBUILD_WEBHOOK_PREV_COMMIT}.car/") ;done
artifacts:
files:
- ./target/*.car
Build works but the commit does not show in the final .car name. I would like to understand why.
Hypothesis n°1: VARs needs to be explicitly sourced
I tried the following without much success
env:
variable:
- COMMIT="${CODEBUILD_WEBHOOK_PREV_COMMIT}"
phases:
install:
commands:
- apt-get update -y
build:
commands:
- echo Entered the build phase...
- echo Build started on `date`
- mvn clean install -Dmaven.test.skip=true
- carpath=./*_CA/target/*.car
- for f in $carpath;do mv -- "$f" $(echo $f | sed -E "s/.car$/_${COMMIT}.car/") ;done
VARs are only available to AWS default build container
I am using Maven's official image maven:3.6.3-jdk-8 instead of Amazon's general purpose build image. Are VARs available for custom images? I can't find any clear indication they are not.

Answer 1

I lost entire afternoon on this, for anyone that is coming here with the same problem, here is how I solved it:
First, I've put printenv in commands to see whats going on and $CODEBUILD_WEBHOOK_PREV_COMMIT env variable was completely missing. But you can use $CODEBUILD_RESOLVED_SOURCE_VERSION instead, which was there!