How to show syntax highlighting for non standard file extensions?

[nbcchen]

I have a file called Jenkinsfile-abc and I want GitHub.com to show it as a Groovy/Jenkinsfile, instead of a plain text file.

In Visual Studio I can use files.associations to achieve syntax highlighting. For GitHub.com I read something about modifying .gitattributtes but it didn't work for me.

[vladlen-codes]

You cannot force GitHub.com to treat Jenkinsfile-abc as a Jenkinsfile/Groovy file using .gitattributes.
However if you're able to rename to .groovy or Jenkinsfile, Github can recognize.
Jenkinsfile-abc -> Jenkinsfile.abc.groovy

[Abdullah-khateeb]

Add a .gitattributes file to the repo with:

Jenkinsfile-* linguist-language=Groovy

Commit and push, then reload the file on GitHub. This forces Groovy/Jenkins syntax highlighting for non-standard Jenkinsfile names.