However, if you are on a unix system you might find the tee utility program usefull

~ 1>whatis tee
tee  (1)  - read from standard input and write to standard output and 
+files
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Says autark:

You could try to define your own print function, sub print { ... }

You can't override print.

I don't see why it has to be called print (this was mentioned as a specific error reporting problem, I believe)...

sub writeError {
  print STDERR @_;
  print FILE @_;
  # yes I know that should be Mail::Mailer, but I don't know its synta
+x
  open MAIL, '|/usr/sbin/sendmail admin' or die;
  print MAIL @_;
  close MAIL;
}
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Assuming FILE is already open and is avalible from there.

This solution also has the advantage of allowing simple and understandable maintainability.

# Usage: $teed_fh = tee @output_handles;
# Returns a new filehandle that, when written, copies to all @output_h
+andles
sub tee {
    use vars qw(*__TEE_FH);
    my $tfh = do { \local *__TEE_FH }; # XXX Should use IO::Handle ins
+tead
    defined( my $pid = open($tfh, "|-") ) or die "fork: $!";
    return select((select($tfh), $| = 1)[0]) if $pid;
    for (@_) { select($_); $| = 1 }
    while( sysread(STDIN, my $block, 8192) ) { print $_ $block for @_ 
+}
    kill 9,$$ or exit; # XXX Should use POSIX::_exit instead
}
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# Tee STDOUT to a log file
use vars qw(*LOG);
open LOG, ">>log.txt" or die "log.txt: $!";
*STDOUT = tee(*STDOUT, *LOG);
END { close STDOUT and wait }

# Now do something that writes to STDOUT
print "Hello, world #$_!\n" for (1..20);

# XXX But, should have just used IO::Tee in first place :)
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