Question

I would like to test whether GNUPlot is installed on the system on which my program is running.
For that, I figured I’ll test for the existence of the gnuplot executable in the user’s install locations through stat() call.

However, I don’t know how to read the $PATH environment variable in C so I can test for the existence of the file in those locations.

Answer 1

To read the PATH environment variable, use getenv("PATH").

However, if you just want to run gnuplot if it’s available, and perform some fallback action if it’s not, then you should just try to run it (e.g. with fork and execvp or posix_spawnp) and handle the failure case.