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IO::Null.3pm

NAME

IO::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"