use IO::Callback; # Here's the coderef my $code = sub { my $str = shift; print STDERR "This is really bad: $str"; }; # Turn it into a filehandle opened in write mode my $fh = IO::Callback->new('>', $code); # Select that filehandle (makes it the default for print, say, etc). select($fh); # Print something - it gets passed to the coderef! print "Hello World\n";