#!/usr/local/bin/perl

##########################
## Just an illustration of file locking.
## This is much safer than just writing.
## However, this example is not perfect.
## The print statement could fail, or
## the original flock might not return.
## A more robust program would take
## this into account.
##

use Fcntl;  # defines constants used by flock

    my $file = '/homes/home8/adabyron/cgi-bin/output';
    $ENV{PATH} = '';
    $ENV{ENV} = '';

    print "Content-type: text/plain\n\n";

    ## Don't let the output file grow arbitrarily.
    if ( -s $file > 4000) {
	print "Sorry, file is too big\n";
	unlink $file;
	exit;
    }	
    else {
	## Print accurate error messages when possible
	unless (open (F, ">>$file") ) {
	    print "Sorry, can't open $file\n";
	    exit;
	}
    }

    flock(F, LOCK_EX);        # get exclusive lock
    print F `/usr/bin/date`;  # write to file
    flock(F, LOCK_UN);        # release lock
    close F;

    print "File has been written\n";