Jenkins: git diff in pipeline to discover modified files

Jenkins-GitDiff.groovy

#!groovy

// https://medium.com/rocket-travel-engineering/running-advanced-git-commands-in-a-declarative-multibranch-jenkinsfile-e82b075dbc53
// Jenkins only checks out the branch for performance reasons so to be able to do more advanced git commands we need to
// also fetch master (or anything else you need)
pipeline {
    agent any
    stages {
        stage ("info") {
            when {
		        changeRequest()
			}
			steps {
				powershell 'gci env:\\ | ft name,value -autosize'
				
                // add a ref to git config to make it aware of master
                powershell '& git config --add remote.origin.fetch +refs/heads/master:refs/remotes/origin/master'
				
                // now fetch master so you can do a diff against it 
                powershell '& git fetch --no-tags'
				
                // do the diff and set some variable based on the result
                powershell '''
					$DiffToMaster = & git diff --name-only origin/master..origin/$env:BRANCH_NAME
					Switch ($DiffToMaster) {
						'server-1607/base.json' {$env:PACK_BASE = $true}
						'server-1607/basic.json' {$env:PACK_BASIC = $true}
						'server-1607/algo.json' {$env:PACK_ALGO = $true}
						'server-1607/build.json' {$env:PACK_BUILD = $true}
						'server-1607/calc.json' {$env:PACK_CALC = $true}
					}
					gci env:/PACK_*
				'''
			}
		}
  }
}

OMG! this is what i was looking for. So good! thank you for putting this out there!

@sphimmer I'm glad this was helpful! Just a word of warning about something I've learnt since and haven't updated here:

There is a subtle difference between origin/master..origin/$env:BRANCH_NAME and origin/master...origin/$env:BRANCH_NAME. Notice the dots. If you want to see the changes exactly as they would appear on a GitHub PR you will want to use ....

See this blog post for a better explanation

Thanks, this helped a lot!