#!c:/perl5/perl
use Fcntl qw(:DEFAULT :flock);
use CGI qw/:standard/;
use strict;

...my content...
sysopen(OUTFILE,$OUTFILE,O_WRONLY);

#LOCK THE FILE
unless(flock(OUTFILE,LOCK_EX)){
   flock(OUTFILE,LOCK_EX) or die;
}