Groovy script to add PR title as a environment variable to Jenkins build environment

PR_title.groovy

// I had the need to access the PR title in a build triggered
// by a merge of that PR into the targeted repository. In our case,
// we use the GitHub hook trigger for GITScm polling setting provided
// by the Github plugin. This fires a webhook at your jenkins instance
// (must be configured in Github) when changes are pushed into the
// target repo. The code below is put into the Groovy script window
// provded by the Environment Injector Plugin.

// Get the current build environment variables.
def thr = Thread.currentThread()
def build = thr?.executable
def envVarsMap = build.parent.builds[0].properties.get("envVars")

// Build the command to extract the commit message using git log.
// Note PR title gets inserted into commit message when PR is merged.
def cmd = "git --git-dir=$envVarsMap.WORKSPACE/.git log --format=%b -1 $envVarsMap.GIT_COMMIT";

// Execute the shell command.
def sout = new StringBuilder(), serr = new StringBuilder()
def proc = cmd.execute()
proc.consumeProcessOutput(sout, serr)
proc.waitForOrKill(1000)

// Inject the new environment variable.
return ['ghprbPullTitle': sout]