Another way to find out if a program is installed is by using the which command. It will show the path of the program you’re searching for. For example if when your searching for apache you can use the following command:
$ which apache2ctl
/usr/sbin/apache2ctl
And if you searching for PHP try this:
$ which php
/usr/bin/php
If the which command doesn’t give any result it means the software is not installed (or is not in the current $PATH):
$ which php
$