Determine changed modules in multi-module Maven Project in GitHub Actions

build-modified-modules.sh

#!/bin/bash
function itemInModules() {
  local e
  for e in ${MODULES}; do
    if [[ "$e" == "$ITEM" ]]; then
      echo "1"
      return 0
    fi
  done
  echo "0"
}
function addItem() {
    if [ "$MODULES" == "" ]; then
      echo "$1"
    else
      echo "$MODULES $1"
    fi
}
# This will only work in a github workflow trigger by a pull request.
PR=$(echo "${{ github.ref_name }}" | grep -o '[[:digit:]]*')
gh pr checkout $PR
CHANGED=$(gh pr diff --name-only)
ALL_MODULES=$(find . -name "pom.xml" -type f -exec dirname '{}' \; | sed 's/\.\///' | sort -r)
MODULES=
for file in $MODIFIED; do
  FILE=$(realpath $file)
  echo "$file was changed"
  for ITEM in $ALL_MODULES; do
    if [[ "$ITEM" != "." ]] && [[ "$file" == *"$ITEM"* ]]; then
      echo "Matched $ITEM"
      HAS_ITEM=$(itemInModules)
      if ((HAS_ITEM == 0)); then
        MODULES=$(addItem "$ITEM")
      fi
      break
    fi
  done
done
# you can export MODULES or use it here to build to modified modules. -amd ensures that dependent modules are also built.
for module in $MODULES; do
  ./mvnw -pl "$ITEM" install -amd
done