Here's a different way to do it. IMHO, the regex it produces will be much easier and make much more sense. 

use strict;
my $email = "myself\@domain.of-my.own";
my $string = "root: myself\@domain.of-my.own";

my $re = inv_str_seq($email);
$string =~ /^root: $re/ and print 1;

sub inv_str_seq {
    my($string) = @_;
    my @c = map { quotemeta($_) } split '', $string;
    my $re = "\n       [^$c[0]] \n";
    $re .= "    | " . join('',@c[0..$_-1]) .  " [^$c[$_]]\n"
        for (1 .. $#c);
    $re = qr/$re/x;
    return qr/$re+ (?:[^$c[0]]|$)/x;
}

[download]

Update: Moved the quotemeta up.

In reply to Re^2: Regex matching a string beginning with "root: " but not containing another string by jryan
in thread Regex matching a string beginning with "root: " but not containing another string by bronto

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