Early exit for CircleCI in monorepos

7 Aug 2019

I've recently had a situation with a monorepo using CircleCI for testing and deployment. Everything was built on every push - native apps, backend deploys etc. This took a lot of time and cost a lot of $. To solve that, I wrote this short script to early exit a CircleCI job unless certain files or directories changed in that git commit.

#!/bin/bash
set -e

# This script makes CircleCI exit a current job if
# the paths passed as an argument haven't changed.
# This is eg used for preventing building native
# builds unless frontend/native or frontend/shared
# have changed.
# 
# Example usage:
# ./exit-if-path-not-changed.sh path/to/dir1 path/to/dir2
# 
# For reference:
# https://gist.github.com/naesheim/18d0c0a58ee61f4674353a2f4cf71475
# https://discuss.circleci.com/t/ability-to-return-successfully-from-a-job-before-completing-all-the-next-steps/12969/4


# 1. Get all the arguments of the script
# https://unix.stackexchange.com/a/197794
PATHS_TO_SEARCH="$*"

# 2. Make sure the paths to search are not empty
if [ -z "$PATHS_TO_SEARCH" ]; then
    echo "Please provide the paths to search for."
    echo "Example usage:"
    echo "./exit-if-path-not-changed.sh path/to/dir1 path/to/dir2"
    exit 1
fi

# 3. Get the latest commit
LATEST_COMMIT=$(git rev-parse HEAD)

# 4. Get the latest commit in the searched paths
LATEST_COMMIT_IN_PATH=$(git log -1 --format=format:%H --full-diff $PATHS_TO_SEARCH)

if [ $LATEST_COMMIT != $LATEST_COMMIT_IN_PATH ]; then
    echo "Exiting this CircleCI job because code in the following paths have not changed:"
    echo $PATHS_TO_SEARCH
    circleci step halt
fi