IO::Tee(3) User Contributed Perl Documentation IO::Tee(3)

IO::Tee - Multiplex output to multiple output handles

use IO::Tee;
$tee = IO::Tee->new($handle1, $handle2);
print $tee "foo", "bar";
my $input = <$tee>;

"IO::Tee" objects can be used to multiplex input and output in two different ways. The first way is to multiplex output to zero or more output handles. The "IO::Tee" constructor, given a list of output handles, returns a tied handle that can be written to. When written to (using print or printf), the "IO::Tee" object multiplexes the output to the list of handles originally passed to the constructor. As a shortcut, you can also directly pass a string or an array reference to the constructor, in which case "IO::File::new" is called for you with the specified argument or arguments.

The second way is to multiplex input from one input handle to zero or more output handles as it is being read. The "IO::Tee" constructor, given an input handle followed by a list of output handles, returns a tied handle that can be read from as well as written to. When written to, the "IO::Tee" object multiplexes the output to all handles passed to the constructor, as described in the previous paragraph. When read from, the "IO::Tee" object reads from the input handle given as the first argument to the "IO::Tee" constructor, then writes any data read to the output handles given as the remaining arguments to the constructor.

The "IO::Tee" class supports certain "IO::Handle" and "IO::File" methods related to input and output. In particular, the following methods will iterate themselves over all handles associated with the "IO::Tee" object, and return TRUE indicating success if and only if all associated handles returned TRUE indicating success:

The following methods perform input multiplexing as described above:

The following methods can be used to set (but not retrieve) the current values of output-related state variables on all associated handles:

The following methods are directly passed on to the input handle given as the first argument to the "IO::Tee" constructor:

Note that the return value of input multiplexing methods (such as "print") is always the return value of the input action, not the return value of subsequent output actions. In particular, no error is indicated by the return value if the input action itself succeeds but subsequent output multiplexing fails.

use IO::Tee;
use IO::File;
my $tee = new IO::Tee(\*STDOUT,
    new IO::File(">tt1.out"), ">tt2.out");
print join(' ', $tee->handles), "\n";
for (1..10) { print $tee $_, "\n" }
for (1..10) { $tee->print($_, "\n") }
$tee = new IO::Tee('</etc/passwd', \*STDOUT);
my @lines = <$tee>;
print scalar(@lines);

Chung-chieh Shan,

As of August 2017, now being maintained by Neil Bowers.

Copyright (c) 1998-2017 Chung-chieh Shan. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perlfunc, IO::Handle, IO::File.

2023-07-26 perl v5.38.0