The London Perl and Raku Workshop takes place on 26th Oct 2024. If your company depends on Perl, please consider sponsoring and/or attending.


PerlIO::Util - A selection of general PerlIO utilities


This document describes PerlIO::Util version 0.72.


        use PerlIO::Util;

    # utility layers

        # open and flock(IN, LOCK_EX)
        $io = PerlIO::Util->open('+< :flock', $file);

        # open with O_CREAT | O_EXCL
        $io = PerlIO::Util->open('+<:creat :excl', $file);

    my $out = PerlIO::Util->open('>:tee', 'file.txt', \$scalar, \*STDERR);
    print $out 'foo'; # print to 'file.txt', $scalar and *STDERR

    # utility routines

    *STDOUT->push_layer(scalar => \$scalar); # it dies on fail
    print 'foo'; # to $scalar

    print *STDOUT->pop_layer(); # => scalar
    print $scalar; # to *STDOUT


PerlIO::Util provides general PerlIO utilities: utility layers and utility methods.

Utility layers are a part of PerlIO::Util, but you don't need to say use PerlIO::Util for loading them. They will be automatically loaded.



Easy interface to flock().

See PerlIO::flock.


Use of O_CREAT without Fcntl.

See PerlIO::creat.


Use of O_EXCL without Fcntl.

See PerlIO::excl.


Multiplex output stream.

See PerlIO::tee.


PerlIO interface to directory functions.

See PerlIO::dir.


Reverse input stream.

See PerlIO::reverse.


Mediation of filesystem encoding.

This layer was split into an independent distribution, PerlIO::fse.

See PerlIO::fse.


PerlIO::Util->open(mode, args)

Calls built-in open(), and returns an IO::Handle instance named args. It dies on fail.

Unlike Perl's open() (nor IO::File's), mode is always required.

PerlIO::Util->known_layers( )

Returns the known layer names.

FILEHANDLE->get_layers( )

Returns the names of the PerlIO layers on FILEHANDLE.

See "Querying the layers of filehandles" in PerlIO.

FILEHANDLE->push_layer(layer [ => arg])

Almost equivalent to binmode(FILEHANDLE, ':layer(arg)'), but accepts any type of arg, e.g. a scalar reference to the :scalar layer.

This method dies on fail. Otherwise, it returns FILEHANDLE.

FILEHANDLE->pop_layer( )

Equivalent to binmode(FILEHANDLE, ':pop'). It removes a top level layer from FILEHANDLE, but note that you cannot remove dummy layers such as :utf8 or :flock.

This method returns the name of the popped layer.


Perl 5.8.1 or later, and a C compiler.


No bugs have been reported.

Please report any bugs or feature requests to <gfuji(at)>, or through the web interface at


PerlIO::flock, PerlIO::creat, PerlIO::excl, PerlIO::tee, PerlIO::dir, PerlIO::reverse, PerlIO::fse.

PerlIO for push_layer() and pop_layer().

perliol for implementation details.

"open" in perlfunc.



Goro Fuji (藤 吾郎) <gfuji(at)>.


Copyright (c) 2008-2010, Goro Fuji <gfuji(at)>. Some rights reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.