Just to propose a TMTOWTDI solution that nobody else suggested yet..

Variables passed to a subroutine are automatically aliased to the @_ array, so if you modify them, you modify the original variables passed in:

use strict;

my ($X, $Y);

modifyvars($X, $Y);
print "after: X=$X, Y=$Y\n";

sub modifyvars {
    $_[0] = 'foo';
    $_[1] = 'bar';

    my $rc = 0;
    $rc = 1 if $_[0] ne 'x';
    return 0;
}
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Though this isn't too easy to read. Using prototypes (mentioned above) is better.