how to Quick Look text files with custom file extensions in Finder When I have .txt files or .py files, I can Quick Look those files in Finder. I have .jl files that are codes written in the Julia Language. Of course they are text files. They will open in a text editor like Sublime Text. How can I Quick Look these .jl files in Finder?
update

With the new macOS release in 2019, the macOS Catalina, this approach is banned.



Install QLStephen, a QuickLook plugin that enables viewing of text files with arbitrary filetypes.

To install, copy the *.qlgenerator file to ~/Library/QuickLook/.