Check out the Sort::Naturally module - it should do what you want. Getting the sort function to do this isn't hard, but it's not entirely straight-forward, either. At least not until you see the 'trick' (which is to separate out the letters from the numbers and find a way to sort on them separately - one way is to use an intermediate string where you insert leading zeros - ca1 becomes ca01, for example). And, of course, understand the trick. ;-) Sort::Naturally encapsulates this in a way that makes it easy even for more advanced monks to not get it wrong.

#!/usr/bin/perl -w

use strict;

my $base = "ca";

my @dirs = map { $base . int (rand 100) } (1..10);

# Instead of matching for $base (ca) you can also match characters etc
+. This approach works for simple things and can get complex quickly
my @sorted = sort { $a->[0] cmp $b->[0] ||
                    $a->[1] <=> $b->[1] } map { [/($base)(\d+)/] } @di
+rs;

@sorted = map { $_->[0] . $_->[1] } @sorted;

print $_, $/ for (@dirs);
print $/;
print $_, $/ for (@sorted);
[download]

Output

ca58
ca43
ca98
ca83
ca11
ca59
ca54
ca92
ca69
ca30

ca11
ca30
ca43
ca54
ca58
ca59
ca69
ca83
ca92
ca98
[download]

See also our wonderful Tutorials section, including the following (in no particular order):

Complex sorting
Understanding transformation sorts (ST, GRT), the details
Resorting to Sorting

Categorized Questions and Answers also has an entire section on sorting. superfrink recently linked to a great sorting reference in this node.

HTH,