What is the best way to do this in perl?

Best way? I don't know if there is a "best way", just lots of ways to do it.

Here is my solution:

#!/usr/bin/perl -w
use strict;
use warnings;
use diagnostics;
                                                                      
+          
my %fn=();
while (my $fnam=<DATA>) {
  chomp $fnam;
  next unless $fnam =~ m@
                       ^(            # Begin capture $1
                         [a-zA-Z]+   # One or more alphas
                         \_          # followed by underscore
                         \d+         # one or more digits
                        )            # End capture $1
                        .*$          # Who cares about the rest
                       @x;
  $fn{$1}++;
}
                                                                      
+          
printf "%s\n",join("\n",sort keys %fn);
exit(0);
__END__
smith_13_503_de7.p
smith_13_502_de7.v
jones_104_503_de7.p
jones_104_502_de7.v
[download]

When run it produces:

--$  perl fnamParse.pl
jones_104
smith_13
--$
[download]