$filelog = "file.log";
open  FILE, $filelog    or die "Can't open $filelog: $!\n";
flock FILE, LOCK_EX     or die "Can't write-lock $filelog: $!\n";
print FILE "$a:$b:$c\n" or die "Can't print to $filelog: $!\n";
close FILE              or die "Can't print to $filelog: $!\n";