#!/your/perl/here

# demonstrate sorting numerically within a string
#
# for example, abc2xyz sorts before abc14xyz
#

use strict;
use warnings;

my @list = map { $_ . "\n" } qw( a1 a2 a10 a1a a2a a10a a01a a10b a1b2c a1b10c aa1 );

print sort mixed_sort @list;

{ # closure for caching, etc.

	my %seen;
	
	sub mixed_sort
	{
		return $seen{$a,$b} if exists( $seen{$a,$b} );

		$seen{$a,$b} = 0;
			
		my $re_num  = qr/\d+/;
		my $re_both = qr/^(\d+|\D+)+$/;

		# split into alpha and numeric fields
		my @x = $a =~ /$re_both/go;
		my @y = $b =~ /$re_both/go;
		
		my $longest = @x > @y ? @x-1 : @y-1;
		
		foreach my $i ( 0..$longest )
		{
			if ( defined( $x[$i] ) and defined( $y[$i] ) )
			{
				if ( ( $x[$i] =~ /^$re_num$/o ) 
				 and ( $y[$i] =~ /^$re_num$/o ) )
				{
					$seen{$a,$b} = $x[$i] <=> $y[$i]; # both are numbers
				}
				else
				{
					$seen{$a,$b} = $x[$i] cmp $y[$i];
				}
			}
			elsif ( defined( $x[$i] ) )
			{
				$seen{$a,$b} = +1;
			}
			elsif ( defined( $y[$i] ) )
			{
				$seen{$a,$b} = -1;
			}
			# else they're both undef, and nothing changes yet
			
			return $seen{$a,$b} if $seen{$a,$b};
		}
		
		return $seen{$a,$b} = $a cmp $b; # if all else fails
	} # end of sub mix_sort

} # end of closure for sub mixed_sort

__END__