# 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 :)