Mastering Perl, 2nd Edition

Chapter 13. Data Persistence

I want my programs to be able to share their data, or even reuse those data on their next run. For big applications, that might mean that I use a database server such as PostgreSQL or MariaDB, but that also means every application needs access to the database, whether that involves getting the permission to use it or being online to reach it. There are plenty of books that cover those solutions, but not many cover the other situations that don’t need that level of infrastructure.

In this chapter, I cover the lightweight solutions that don’t require a database server or a central resource. Instead, I can store data in regular files and pass those around liberally. I don’t need to install a database server, add users, create a web service, or keep everything running. My program output can become the input for the next program in a pipeline.

Perl-Specific Formats

Perl-specific formats output data that makes sense only to a single programming language and are practically useless to other programming languages. That’s not to say that some other programmer can’t read it, just that they might have to do a lot of work to create a parser to understand it.

pack

The pack built-in takes data and turns it into a single string according to a template that I provide. It’s similar to sprintf, although as the pack name suggests, the output string uses space as efficiently as it can:

#!/usr/bin/perl # pack.pl my $packed = pack( 'NCA*', 31415926, 32, 'Perl' ); ...