Check the App::Info namespace to see one way to check to see if programs are installed. I'm sure that the author wouldn't mind new programs being handled by it.

And the use of $ENV{PATH} will cause an error with taint checking because Perl marks "unsafe" data as tainted when in taint mode. "unsafe" data is essentially any data that was not explicitly set (or untainted) by the Perl executable. Since Perl doesn't know who set the environment variables, it has no way of knowing that some malicious hacker hasn't added /usr/bin/malicious/ to your path. See perlsec for more information.