[jwilk]

You shouldn't assume grep is in /usr/bin. On many systems it's in /bin.

Perl's exec and Python's subprocess already search for executables in PATH, so you don't need to provide the full path.

In C, you can use execvp() instead of execv().

(No idea about PHP…)

[okdana]

Right, it was just a random example that popped into my head. You would probably also want to think twice about using -R (at least with GNU grep), about hard-coding the search directory, &c.

All of PHP's process-execution methods (except one, which is unusable on many systems) go through the shell, so by virtue of that it also searches the PATH.