IO::Null(3) User Contributed Perl Documentation IO::Null(3)NAMEIO::Null-- class for null filehandles
SYNOPSIS
use IO::Null;
my $fh = IO::Null->new;
print $fh "I have nothing to say\n"; # does nothing.
# or:
$fh->print("And I'm saying it.\n"); # ditto.
# or:
my $old = select($fh);
print "and that is poetry / as I needed it --John Cage"; # nada!
select($old);
Or even:
tie(*FOO, IO::Null);
print FOO "Lalalalala!\n"; # does nothing.
DESCRIPTION
This is a class for null filehandles.
Calling a constructor of this class always succeeds, returning a new
null filehandle.
Writing to any object of this class is always a no-operation, and
returns true.
Reading from any object of this class is always no-operation, and
returns empty-string or empty-list, as appropriate.
WHY
You could say:
open(NULL, '>/dev/null') || die "WHAAT?! $!";
and get a null FH that way. But not everyone is using an OS that has a
"/dev/null"
IMPLEMENTATION
This is a subclass of IO::Handle. Applicable methods with subs that do
nothing, and return an appropriate value.
SEE ALSO
IO::Handle, perltie, IO::Scalar
CAVEATS
* This:
use IO::Null;
$^W = 1; # turn on warnings
tie(*FOO, IO::Null);
print FOO "Lalalalala!\n"; # does nothing.
untie(*FOO);
has been known to produce this odd warning:
untie attempted while 3 inner references still exist.
and I've no idea why.
* Furthermore, this:
use IO::Null;
$^W = 1;
*FOO = IO::Null->new;
print FOO "Lalalalala!\n"; # does nothing.
close(FOO);
emits these warnings:
Filehandle main::FOO never opened.
Close on unopened file <GLOB>.
...which are, in fact, true; the FH behind the FOO{IO} was never opened
on any real filehandle. (I'd welcome anyone's (working) suggestions on
how to suppress these warnings.)
You get the same warnings with:
use IO::Null;
$^W = 1;
my $fh = IO::Null->new;
print $fh "Lalalalala!\n"; # does nothing.
close $fh;
Note that this, however:
use IO::Null;
$^W = 1;
my $fh = IO::Null->new;
$fh->print("Lalalalala!\n"); # does nothing.
$fh->close();
emits no warnings.
* I don't know if you can successfully untaint a null filehandle.
* This:
$null_fh->fileno
will return a defined and nonzero number, but one you're not likely to
want to use for anything. See the source.
* These docs are longer than the source itself. Read the source!
COPYRIGHT
Copyright (c) 2000 Sean M. Burke. All rights reserved.
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
AUTHOR
Sean M. Burke "sburke@cpan.org"
perl v5.14.0 2004-12-30 IO::Null(3)
