sub open_file 
{
    my $file = shift || return;
    
    my $lock     = 0;
    my $compress = shift;

    my $fh;

    if($compress) { 
        use IO::Zlib;
        $fh = IO::Zlib->new($file, 'rb') 
            or die "Couldn't open file: $!\n";
    }
    else {
        open($fh, '<', $file) or die "Couldn't open file: $!\n";
    }
    
    if($lock) {
        use Fcntl qw(:DEFAULT :flock);
        flock($fh, LOCK_SH) or die "Couldn't lock file: $!\n";
    }

    return $fh;
}
[download]

The above will fail if you want to both lock and decompress the file. This is somewhat obvious, since when $fh is inititlized using IO::Zlib, it doesn't really hold a file descriptor.

I've also tried using the tie interface on IO::Zlib instead of calling IO::Zlib->new():

tie $fh, 'IO::Zlib', $file, "rb";
[download]

But this fails with a message Can't use string ("IO::Zlib") as a symbol ref while "strict refs" in use at /usr/local/lib/perl5/site_perl/5.8.0/IO/Zlib.pm line 317. Bug in my code or in IO::Zlib?

Doing it via tie or IO::Zlib->new() or some other clever way is fine by me, as long as you can do both locking and transparent decompression.