Unlike what cchampion is saying, you can do it in one regex, and even without using alternation and /g. A short benchmark even suggest it to be slightly faster than using two regexes. The regex:

    s!^/*(.*[^/])/*$!/$1/!;
[download]

The benchmark:

#!/usr/bin/perl

use strict;  
use warnings;

use Benchmark qw /timethese cmpthese/;

chomp (our @lines = <DATA>);

our (@r1, @r2, @r3);
cmpthese -10 => {
    mikedshelton  =>  '@r1 = map {local $_ = $_;
                                  s!^/*!/!;
                                  s!/*$!/!;   
                                  $_} @lines',  
    cchampion     =>  '@r2 = map {local $_ = $_;
                                  s{ (?: ^ /* | (?<=[^/])/* $ ) }</>xg
+;
                                  $_} @lines',  
    abigail       =>  '@r3 = map {local $_ = $_;
                                  s!^/*(.*[^/])/*$!/$1/!;
                                  $_} @lines',
};

die "Unequal\n" unless "@r1" eq "@r2" && "@r2" eq "@r3";

__END__
/foo/bar/baz/
foo/bar/baz/
/foo/bar/baz
foo/bar/baz
/
foo/bar
foo
[download]

And the results:

                Rate    cchampion mikedshelton      abigail
cchampion     8069/s           --         -20%         -27%
mikedshelton 10038/s          24%           --          -9%
abigail      11057/s          37%          10%           --
[download]

Abigail