NAME

SYNOPSIS

        open my $out, '>>:tee', $file, @sources;

        $out->push_layer(tee => $file);
        $out->push_layer(tee => ">> $file");
        $out->push_layer(tee => \$scalar);
        $out->push_layer(tee => \*FILEHANDLE);

DESCRIPTION

You can use "push_layer()" (defined in "PerlIO::Util") to add a source to a filehandle. The source may be a file name, a scalar reference, or a filehandle. For example:

        $fh->push_layer(tee => $file);    # meaning "> $file"
        $fh->push_layer(tee => ">>$file");# append mode
        $fh->push_layer(tee => \$scalar); # via :scalar
        $fh->push_layer(tee => \*OUT);    # shallow copy, not duplication

You can also use "open()" with multiple arguments. However, it is just a syntax sugar to call "push_layer()": One ":tee" layer has a single extra output stream, so arguments "$x, $y, $z" of "open()", for example, prepares a filehandle with one default layer and two ":tee" layers with a internal output stream.

        open my $tee, '>:tee', $x, $y, $z;
        # the code above means:
        #   open my $tee, '>', $x;
        #   $tee->push_layer(tee => $y);
        #   $tee->push_layer(tee => $z);

        $tee->get_layers(); # => "perlio", "tee($y)", "tee($z)"

        $tee->pop_layer();  # "tee($z)" is popped
        $tee->pop_layer();  # "tee($y)" is popped
        # now $tee is a filehandle only to $x

EXAMPLE

        #!/usr/bin/perl -w
        # Usage: $0 files...
        use strict;
        use PerlIO::Util;

        *STDOUT->push_layer(tee => $_) for @ARGV;

        while(read STDIN, $_, 2**12){
                print;
        }
        __END__

SEE ALSO

AUTHOR

LICENSE AND COPYRIGHT

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