You should think about using DBM. The most common flatfile-DB is the "DB" (Berkeley DB library). The necessary modules are installed on most systems. Just try the following:

use DB_File;
dbmopen %hash, $file, 0666 or die "This is my very own error-message: 
+$!\n";

$value = $hash{'key'}; # get data
$hash{'key'} = $value; # put data
delete $hash{'key'};   # delete data

dbmclose %hash;
[download]

There are a lot different flat-file Databases and you might need another one for your needs. More Information can be found online at CPAN or in O'Reilly's "The Perl Cookbook", Chapter 14 (page 489)
Regards, octopus
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