Generate unique file handles

alih110 has asked for the wisdom of the Perl Monks concerning the following question:

Hello, I want to open a file with a unique filehandle everytime it needs to be opened. Will the following work? => ----------------------

$seed = (time() ^($$ + ($$ <<15)));
$fh = "FH_TEST".$seed;
open (local $fh, "test.out");
while (<$fh>) {
    ..............
    ..............
}
close $fh;
[download]

---------------------- Background: The above code is in a perl module whose multiple instances are running in parallel through LSF. So each call of the module should generate a unique file handle with which to open the same file in read mode.

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Re: Generate unique file handles by moritz (Cardinal) on Aug 20, 2008 at 07:17 UTC
Why not simply use a lexical variable as the file handle? `open my $fh, '<', 'test.out' or die "Can't open test.out: $!";` [download] I don't think your approach works - did you try it?	[reply] [d/l]
Re^2: Generate unique file handles by alih110 (Novice) on Aug 20, 2008 at 08:23 UTC
I have not yet tried it. Following is the issue faced with a fixed file handle name => Since the perl module is called in parallel through LSF, suppose one process finishes reading the file and closes the filehandle while another process is still reading the file, this file handle also gets closed and it never reads the file completely. Thats why I wanted to have unique file handle names. Can I try $fh_$$ so that it generates a unique file handle with process id?	[reply]
Re^3: Generate unique file handles by moritz (Cardinal) on Aug 20, 2008 at 08:28 UTC
If LSF starts a new process for each job (and only in this case `$$` will actually help you) it's not an issue at all, because perl variables aren't shared across processes. In this case you can even use bare word file handles, although I don't recommend them. Even if it uses perl threads, there's no need to worry because variables aren't shared by default. (As a side node when you think of a variable variable name, use a hash instead. So instead of the non-working `$fh_$$` you'd use `my %handles; $handles{$$} = ...` instead. But as said above, no need here).	[reply] [d/l] [select]
Re: Generate unique file handles by Anonymous Monk on Aug 20, 2008 at 07:15 UTC
`use Symbol; $sym = gensym; open($sym, "filename"); $_ = <$sym>;` [download]	[reply] [d/l]
Re: Generate unique file handles by bruno (Friar) on Aug 20, 2008 at 19:13 UTC
I highly recommend you the File::Temp module.	[reply]
Re: Generate unique file handles by ikegami (Patriarch) on Aug 21, 2008 at 20:06 UTC
`local $fh` erases the content of `$fh`. And even if it didn't, `open` doesn't takea variable name for its first argument (just a variable). You can simply use `open(my $fh, '<', 'test.out')` [download] Open returns a new anonymous file handle in $fh every time.	[reply] [d/l] [select]