How to call an external program?

[iahung3]

For example, clang-format. I'm finding a code formatter plugin for Geany. But all of the projects I encountered are unmaintained.

[elextr]

You don't need a plugin. Since clang-format can act as a filter (read stdin and write stdout) it can be run from a custom command and format the selection, or the whole file if no selection.

Same for any other formatter that acts as a filter.