open(FH,"+<./file.dat") || die("Can't open ./file.dat for reading/writing: $!");
flock(FH,LOCK_EX);
seek(FH,0,0);
@dat = <FH>;
foreach (@dat) {chomp}
# this is where I process @dat, and when I feed text 
# manually into it, it works.  the problem doesn't
# lie in this segment of the code
seek(FH,0,0);
print FH join("\n",@dat);
flock(FH,LOCK_UN);
close(FH);