CircleCi - only build features that has changed

build_directory.sh

set -e

# latest commit
LATEST_COMMIT=$(git rev-parse HEAD)

# latest commit where path/to/folder1 was changed
FOLDER1_COMMIT=$(git log -1 --format=format:%H --full-diff path/to/folder1)

# latest commit where path/to/folder2 was changed
FOLDER2_COMMIT=$(git log -1 --format=format:%H --full-diff path/to/folder2)

if [ $FOLDER1_COMMIT = $LATEST_COMMIT ];
    then
        echo "files in folder1 has changed"
        .circleci/do_something.sh
elif [ $FOLDER2_COMMIT = $LATEST_COMMIT ];
    then
        echo "files in folder2 has changed"
        .circleci/do_something_else.sh
else
     echo "no folders of relevance has changed"
     exit 0;
fi

config.yml

version: 2
jobs:
    build:
        docker:
            - image: circleci/...
        steps:
            - checkout
            - run:
                command: |
                    .circleci/build_directory.sh

The idea is that the actual CircleCI job only runs a shell script. The shell script then checks which folders have been effected with the commit using regular git commands.

The git commands then figure out which folder (service/lib) has been changed and does the relevant build steps.