My proposal is to first normalize the input string to the form "start-end" using substitutions. This is simple if the string conforms to the specification. (I also assume that a pure "-" means a list from zero to the maximum.) Once this normalization is achieved, it is very simple to build the list: 

use strict;
use warnings;

sub range_to_list {
  my ($max, $str) = @_;
  $str =~ s/^-/0-/;         # string starts with -
  $str =~ s/-$/-$max/;      # string ends with -
  $str =~ s/^(\d+)$/$1-$1/; # just a number
  return ($str =~ /^(\d+)-(\d+)$/)&&($1<=$max)&&($2<=$max) ? ($1..$2) 
+: ();
}

my @tests = qw( 4 4-6 5- -2 - a 11- 2-7w -11 );

for my $test (@tests) {
  my @list = range_to_list 10, $test;
  print "$test:\t@list\n";
}

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

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