If you have installed multiple versions of an application into your system, you may wonder which command is being run from the command line when you launch it. This is especially useful to figure out the path of php when running on a shared server, as many shared servers have both php4 and php5 installed.

which <commandname>

To find the path of the application, you can use the which command, followed by the executable that you would have run.

Example:

# which svn
/usr/bin/svn

# which php
/usr/local/bin/php