How do you 'tee' the STDOUT?

/usr/bin/tee

a snippet of Perl code

# replicate everything that goes to STDOUT to a file too  (uses a forked subprocess)
use autodie;
sub tee {
    my ($filename) = @_;
    open my $origstdout, '>&STDOUT';
    open my $fh, ">$filename";
    if (!open STDOUT, '|-') {
        ## child process
        while (sysread(STDIN, my $buffer, 1024)) {
            syswrite($origstdout, $buffer);
            syswrite($fh, $buffer);
        }
        exit;
    }
    ## parent process continues on and returns
    close $origstdout;
    close $fh;
}

CPAN modules

• using basic Perl and the external 'tee' utility:
  • perlfaq5
  • [2]
• PerlIO::tee (example) [2] [3]
• IO::Tee (example)
• IO::Pager
• File::Tee
• Tie::FileHandle::MultiPlex
• Tee::App — I dunno, it seems a lot more complicated than the snippet above