My rule of thumbs: Whenever I feel like it, I'll write simple stuff with bash. If it takes 10 lines or so, it's not simple anymore (for me), so Perl takes over. If it takes command line switches, it's not something simple (for me) too, so Perl takes over as well. For simple switches I'll just use -s switch because it's simple and nice. However, for rather complex switches I'll turn to the standard Getopt::Long.