my $file = "output.txt";
open (FOO, "> $file") or die "Cannot write '$file': $!";
select(FOO);
# Do stuff here during which default prints go to the file.
# BUT: print STDOUT $string; will still go to STDOUT.  It
# isn't gone, just ignored by default.
select(STDOUT);
# If you are going to do a bunch more stuff.
close (FOO);
# prints here are back to normal.