open STDOUT, ">>$dir/TEST.NEW" or exit 1;
open STDERR, ">>&STDOUT" or exit 2;
flock STDOUT, LOCK_EX | LOCK_NB or exit 3;
truncate STDOUT, 0; # delete everything from the file

# The remainder of the program will be writing to an
# empty file.  

close STDERR;
close STDOUT;