• Standard files are opened automatically
• STDIN is standard input
• STDOUT is standard output
• STDERR is standard error output
• Can re-open these for special handling
• print uses standard output by default
• die and warn use standard error by default

        print STDOUT "Hello, world.\n";  # STDOUT not needed

        open STDERR, ">> logfile" or die "Can't redirect errors to log: $!";
        print STDERR "Oh no, here's an error message.\n";
        warn "Oh no, here's another error message.\n";
        close STDERR;