circleCI - How to run job when has change in specific directory

Question

I'm using circleCI version 2 and my config.yml like this:

version: 2
jobs:
   a:
     steps:...
   b:
     steps:...
workflows:
  version: 2
  main_pipeline:
    jobs:
       - a
       - b

I want only to build when a change happens in the directory.

job a for folder a job b for folder b

when folder a changes, build only job a.

Answer 1

function trigger_job() {
    job_name=$1
    curl --user ${CIRCLE_API_TOKEN}: \
        --data build_parameters[CIRCLE_JOB]=$job_name \
        --data revision=$CIRCLE_SHA1 \
https://circleci.com/api/v1.1/project/github/$CIRCLE_PROJECT_USERNAME/$CIRCLE_PROJECT_REPONAME/tree/$CIRCLE_BRANCH

I use this function for trigger job and find different by git-diff like this git diff-tree --name-only $(git log -n 2 --pretty=format:"%H") | grep project