If you have Perl version 5.10+, the  (?|pattern) construct (see Extended Patterns in perlre) supports a neat approach: 

c:\@Work\Perl>perl -wMstrict -le
"use 5.010;
 ;;
 use Test::More 'no_plan';
 use Test::NoWarnings;
 ;;
 my $rx_rng = qr{ \A (?| (\d*) - (\d+) | (\d+) - (\d*)) \z }xms;
 ;;
 my $max = 10;
 ;;
 for my $ar_vector (
   [ '0-0', 0..0 ], [ '4-6', 4..6 ], [ '-2', 0..2 ], [ '3-', 3..$max ]
+,
   ) {
   my ($rs, @rng) = @$ar_vector;
   is_deeply [ range($rs, $max, $rx_rng) ], \@rng, qq{'$rs'};
   }
 ;;
 sub range {
   my ($rs, $r_max, $rx) = @_;
   ;;
   my ($lo, $hi) = $rs =~ $rx or die qq{not a range: '$rs'};
   $lo = 0      unless length $lo;
   $hi = $r_max unless length $hi;
   ;;
   die qq{range inverted: '$rs'}   if $lo > $hi;
   die qq{max out of range: '$rs'} if $hi > $r_max;
   ;;
   return $lo .. $hi;
   }
"
ok 1 - '0-0'
ok 2 - '4-6'
ok 3 - '-2'
ok 4 - '3-'
ok 5 - no warnings
1..5

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I will leave you to test the exceptions.

Give a man a fish:  <%-(-(-(-<

In reply to Re: Specifying a range of indices via the command line by AnomalousMonk
in thread Specifying a range of indices via the command line by eyepopslikeamosquito

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