#!/usr/local/bin/perl

##########################
## Just an illustration of file locking.
## This time, with a DBM file.
## This illustration is a simplified version from
## the DB_File man page.  If you don't understand
## the perl here, just skip it for now.
##

use Fcntl;  # defines constants used by flock
use DB_File;

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

    $netid = $ENV{REMOTE_USER} ? $ENV{REMOTE_USER} : 'nobody';

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

    my $fh = tie ( %h, 'DB_File', $file, O_CREAT|O_RDWR, 0600 );
    unless ($fh) {
	print "Can't open $file\n";
	exit;
    }

    ## get file descriptor
    my $fd = $fh->fd;

    ## open a file handle corresponding to file descriptor
    open (DB, "+<&=$fd");

    ## Now lock file handle for writing
    flock(DB, LOCK_EX); 

    ## Write file by assigning to hash
    $h{$netid} = `/usr/bin/date`;

    ## Sync buffer
    $fh->sync;

    ## Unlock file
    flock(DB, LOCK_UN);

    ## Clean up.
    undef $fh;           
    untie %h;
    close DB;

    print "File has been written\n";