How to mark a build unstable in Jenkins when running shell scripts

It can be done without printing magic strings and using TextFinder. Here's some info on it.

Basically you need a .jar file from http://yourserver.com/cli available in shell scripts, then you can use the following command to mark a build unstable:

java -jar jenkins-cli.jar set-build-result unstable

To mark build unstable on error, you can use:

failing_cmd cmd_args || java -jar jenkins-cli.jar set-build-result unstable

The problem is that jenkins-cli.jar has to be available from shell script. You can either put it in easy-to-access path, or download in via job's shell script:

wget ${JENKINS_URL}jnlpJars/jenkins-cli.jar

Use the Text-finder plugin.

Instead of exiting with status 1 (which would fail the build), do:

if ($build_error) print("TESTS FAILED!");

Than in the post-build actions enable the Text Finder, set the regular expression to match the message you printed (TESTS FAILED!) and check the "Unstable if found" checkbox under that entry.

Modern Jenkins versions (since 2.26, October 2016) solved this: it's just an advanced option for the Execute shell build step!

You can just choose and set an arbitrary exit value; if it matches, the build will be unstable. Just pick a value which is unlikely to be launched by a real process in your build.