Find out if a command exists on POSIX system

Question

I want to be able to tell if a command exists on any POSIX system from a shell script.

On Linux, I can do the following:

if which ; th         


        

Answer 1

You could read the stdout/stderr of "which" into a variable or an array (using backticks) rather than checking for an exit code.

If the system does not have a "which" or "where" command, you could also grab the contents of the $PATH variable, then loop over all the directories and search for the given executable. That's essentially what which does (although it might use some caching/optimization of $PATH results).