Based on your comments this may work (UNTESTED):

my $y     = 'aaa';
my $unzip = 'zcat';
my $dir   = '<PATH>';

opendir my $DH, $dir or die "Cannot open directory '$dir' because: $!"
+;

foreach my $path ( map "$dir/$_", readdir $DH ) {
    my ( $exact, $not_exact );
    open my $PIPE, '-|', $unzip, $path or die "Cannot open pipe from '
+$unzip' because: $!";
    while ( <$PIPE> ) {
        if ( /$y/ ) {
            $exact = 1;
            last;
            }
        if ( /($y)/i ) {
            $not_exact = $1;
            }
        }
    close $PIPE or warn $! ? "Error closing '$unzip' pipe: $!"
                           : "Exit status $? from '$unzip'";
    if ( ! $exact && defined $not_exact ) {
        $y = $not_exact;
        }
    }
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