is filehandler used ?

[jeanluca]

Dear Monks,

How can I tell if a filehandler is used, for example, the following code does not work

if ( OUT ) {

}

Any suggestions ?

Thanks a lot
Luca

[Fletch]

How (Not) To Ask A Question

What "doesn't work"? What do you mean by "filehandler is used"? What did you expect that to do? Why would you expect it to do that? How much wood would a woodchuck chuck if a woodchuck could chuck wood?

[Tanktalus]

First, my confusion: "filehandler" is something that handles files, and "filehandle" is a handle to a (or token for a) file. You have a filehandle.

Second, the solution: Using fileno works fine for files. On Linux/unix, it probably works for sockets, fifos, and many other things. On no platform does it work for IO::String or handles to a string buffer (e.g., open OUT, '>', \$buffer). If you are only worried about real files, that's fine.

Instead, you will pretty much need to keep the state seperate. For example, using a symref:

my $fh;
open $fh, "<", "/etc/shadow" or $fh = undef;
if ($fh) {
  # do stuff
}

Now it doesn't matter what you have that you're reading from - failure results in an undef. (Not quite true - if you start using the forking version of open, such as "-|" or "|-", then things have to work a bit differently.)

Personally, I just merge it all:

if (open my $fh, "<", "/etc/shadow")
{
  # do stuff.
  close $fh;
}

Anywhere inside the if, the filehandle is good. Anywhere outside, the filehandle doesn't even exist.

[jeanluca]

Ok, here is the situation, if the filehander is used, I would like to use it


if ( OUT ) {
    print OUT " bla bla\n" ;
}

unfortunately, if ( OUT ) is always true!!
Hopefully this makes sense

Luca

[Kanji]

if (defined fileno(OUT)) {
    print OUT "bla bla\n";
}

[beachbum]

any idea of the diff between yours and mine? I've always used *HANDLE:

use strict;
use warnings;
open(OUT, ">test.txt") or die "Can't open file to write, $!.";
if(defined fileno *OUT){
    print "File handle is valid.";
}else{
    print "Nope.";
}
close OUT;

[ambrus]

if (*STDOUT{IO}) {
    print "it's used\n";
}