Perl for Web Site Management

A DBM Example Script

Let’s take a look at a more complete example. Example 20-1 demonstrates how we might use GDBM_File in an actual script. Like all the examples in this book, it can be downloaded from the book’s web site, at http://www.elanus.net/book/.

Example 20-1. A simple GDBM_File example

#!/usr/bin/perl -w

# color.plx - demonstrate GDBM_File

use strict;

use GDBM_File;
my $datafile = 'color.gdbm';

tie my %COLOR, 'GDBM_File', $datafile, &GDBM_WRCREAT, 0644
    or die "can't tie to $datafile for WRCREAT access: $!";

$COLOR{banana} = 'yellow';
$COLOR{apple}  = 'red';
$COLOR{orange} = 'orange';

untie %COLOR; # no longer tied to the DBM file

%COLOR = (  );  # empty the hash, to prove we're really storing
              # the data on disk.

tie %COLOR, 'GDBM_File', $datafile, &GDBM_READER, 0644
    or die "can't tie to $datafile for READER access: $!";
    
print "Here are all the records currently stored in $datafile:\n\n";

while (my($key, $value) = each %COLOR) {
    print "key: '$key', value: '$value'\n";
}

untie %COLOR;

If we run this script, it should produce output that looks like the following:

[jbc@andros jbc]$ color.plx
Here are all the records currently stored in color.gdbm:

key: 'orange', value: 'orange'
key: 'banana', value: 'yellow'
key: 'apple', value: 'red'

Suppose that we now add the following statement immediately after the first tie statement in color.plx, before the %COLOR hash has been untied:

tie my %ANOTHER, 'GDBM_File', $datafile, &GDBM_WRCREAT, 0644 or die "can't tie to $datafile for WRCREAT ...