How can I parse command-line switches in Perl?

Question

In order to extend my "grep" emulator in Perl I have added support for a -r switch which enables recursive searching in sub-directories. Now the command line invocation looks something like this:

perl pgrep.pl -r <directory> <expression>

Both -r and the directory arguments are optional (directory defaults to '.'). As of now I simply check if the first argument is -r and if yes set the appropriate flag, and scan in the rest two arguments using the shift operation. This obviously would be a problem if -r were to appear at the end of the argument list or worse still - in between the directory name and the search expression.

One workaround would be to simply delete the -r item from the @ARGV array so that I can simply shift-in the remaining arguments, but I can't figure out a way to do it without getting an 'undef' in an odd position in my array. Any suggestions or different strategies that you might have used are welcome.

Answer 1

You should be using GetOpt::Long. This will do everything you need as described.

Answer 2

use Getopt::Std;

our $opt_r; # will be set to its value if used.
getopts('r:'); # -r has an option.

Answer 3

• Add a -d switch for your directory. My opinion is, "if a command is optional it should have a switch to enable it."
• Also I would remove the switches(and their arguments) from the array as I read them, leaving just my "expression". If there's more than 1 element in that array, someone wrote something wrong.

Answer 4

My chapter on "Configuration" in Mastering Perl goes through several possibilities for command-line switch processing, from perl's -s to the popular modules for handling these. For your example, I'd probably start with Getopt::Std and convert to Getopt::Long if I needed it later.

Good luck, :)