sub find_string {
    my ( $file, $string, $negative ) = @_;
    return 1
        if _find_string( $file, $string, $negative )
    die "False :Test result is FAIL";
}

sub find_without_string {
    $_[2] = 1;
    goto &find_string;
}

sub _find_string {
    my ($file, $string, $negative) = @_;
    open my $fh, '<', $file;
    while (<$fh>) {
        return !$negative if /\Q$string/;
    }
    return $negative;
}

# Original functionality
find_string('search.txt', 'name: abc ');

# Inverted functionality
find_string('search2.txt', 'name: abc ', 1 );
# or
find_without_string('search2.txt', 'name: abc ' );