Glad to hear you have a working solution. Might I also suggest that for test scripts like this you consider using one of the Test::* frameworks? They will help to highlight where your matches fail. Here's an example using the ubiquitous Test::More to show how simple it would be to integrate.

#!/usr/bin/perl
use strict;
use warnings;
use Test::More;

# Set up source strings (keys) and expected results (values)
my %tests = (
    '"abcd\\\\efgh"'     => 'abcd\\\\efgh',
    '"abcd\\""'          => 'abcd\\"',
    '"abcd\\"efgh"'      => 'abcd\\"efgh',
    '"abcd\\\\\\"efgh"'  => 'abcd\\\\\\"efgh',
    '"abcd\\\\i\\"efgh"' => 'abcd\\\\i\\"efgh',
    '"abcd\\\\"'         => 'abcd\\\\'
);

# Set the total number of tests to perform
plan tests => 3 * keys %tests;

while ( my ($test, $exp) = each %tests) {
    ok ($test =~ /^"((?:[^"\\]|\\["\\])+)"$/, "$test matches");
    is ($1, $exp, "\$1 is $exp");
    is ($2, undef, '$2 is undefined');
}
[download]

If any of the tests fail it is easier to spot than having to visually parse the script output. You can also run prove on the script to get just a summary which is even clearer.

If you write a lot of scripts like this, it is well worth becoming familiar with the wealth of testing modules available.