Re: how to close all files

There's always the BFI method: start at 0, create a filehandle for that descriptor, close it, increment and repeat until you reach a maximum (there's probably a way to tickle the maximum possible file descriptor number out of POSIX but I can't recall it offhand and my copy of APUE isn't readily available).

use constant MAX_DESCRIPTORS => 255;
for my $fd_no ( 0 .. MAX_DESCRIPTORS() ) {
  open( my $fh, ">>&=", $fd_no ) or warn "Can't dup FD $fd_no: $!\n";
  close( $fh );
}
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Update: Dur, never mind me. The correct mechanism is POSIX::close as is mentioned below, not dup'ing. MENTAL NOTE: NO POSTING BEFORE CAFFEINE . . .

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The cake is a lie.
The cake is a lie.

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Re^2: how to close all files by mr_mischief (Monsignor) on Oct 23, 2008 at 23:41 UTC
I think there's some misunderstanding of what a duplicate filehandle does. What you have is very nice for closing the duplicates. It doesn't close the originals, though. Duplicate file handles to the same descriptor may share lock status, but they still open and close separately. I did test this with 255 instead of 20 BTW, but you don't really need to see 255 warnings scroll by. There are fewer than 20 files open here, anyway. Just call it the "arbitrarily large" constant people have been tossing out. If you really want to close by descriptor, use `POSIX::close` as suggested by BrowserUk at Re: how to close all files. use strict; use warnings; open ( my $foo, '>&=', 1 ); close( STDOUT ); print STDOUT "foo!\n"; print $foo "foo!\n"; open ( my $bar, '>&=', $foo ); close $foo; print $foo "foo!\n"; print $bar "bar!\n"; open ( my $baz, '>', 'files/baz' ); open ( my $quux, '>&=', $baz ); close $baz; print $quux "quux!\n"; open ( $baz, '>>', 'files/baz' ); open ( $quux, '>>&=', $baz ); close $quux; print $baz "baz!\n"; open ( my $prefork, '>', 'files/prefork.txt' ); if ( my $kidpid = fork ) { my $deadkid = wait(); print $prefork "child was pid $deadkid, which thankfully matches $ +kidpid (we'd be worried if it didn't)\n"; } elsif ( defined $kidpid ) { for ( 0..20 ) { open ( my $postfork, '>>&=', $_ ); close $postfork; print $postfork "Whee!\n"; } print $prefork "Dupes are just copies!\n"; } else { print "I couldn't fork!\n"; } [download]	[reply] [d/l] [select]

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Re^2: how to close all files
by mr_mischief (Monsignor) on Oct 23, 2008 at 23:41 UTC

I think there's some misunderstanding of what a duplicate filehandle does. What you have is very nice for closing the duplicates. It doesn't close the originals, though. Duplicate file handles to the same descriptor may share lock status, but they still open and close separately.

I did test this with 255 instead of 20 BTW, but you don't really need to see 255 warnings scroll by. There are fewer than 20 files open here, anyway. Just call it the "arbitrarily large" constant people have been tossing out.

If you really want to close by descriptor, use POSIX::close as suggested by BrowserUk at Re: how to close all files.

use strict;
use warnings;

open ( my $foo, '>&=', 1 );
close( STDOUT );
print STDOUT "foo!\n";
print $foo "foo!\n";

open ( my $bar, '>&=', $foo );
close $foo;
print $foo "foo!\n";
print $bar "bar!\n";

open ( my $baz, '>', 'files/baz' );
open ( my $quux, '>&=', $baz );
close $baz;
print $quux "quux!\n";

open ( $baz, '>>', 'files/baz' );
open ( $quux, '>>&=', $baz );
close $quux;
print $baz "baz!\n";

open ( my $prefork, '>', 'files/prefork.txt' );

if ( my $kidpid = fork ) {
    my $deadkid = wait();
    print $prefork "child was pid $deadkid, which thankfully matches $
+kidpid (we'd be worried if it didn't)\n";
} elsif ( defined $kidpid ) {
    for ( 0..20 ) {
        open ( my $postfork, '>>&=', $_ );
        close $postfork;
        print $postfork "Whee!\n";
    }
    print $prefork "Dupes are just copies!\n";
} else {
    print "I couldn't fork!\n";
}
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