Mastering Perl

Chapter 14. Data Persistence

My programs can share their data, either with other programs or with future invocations of themselves. To make that possible, I store the data outside of the program’s memory and then read it from that source to recreate it. I can put that data in a file or a database, send it over a network connection, or anything else I want to do with it.

I can even share data between different programs. For anything except for simple applications, I’d probably want to use a robust database server and the DBI module. I won’t cover proper database servers such as MySQL, PostgreSQL, or Oracle. Perl works with those through DBI, and there’s already a great book for that in Further Reading,” at the end of the chapter. This chapter is about lightweight techniques I can use when I don’t need a full server backend.

Flat Files

Conceptually and practically, the easiest way to save and reuse data is to write it as text to a file. I don’t need much to do it, and I can inspect the file, change the data if I like, and send it to other people without worrying about low-level details like byte ordering or internal data sizes. When I want to reuse the data, I read it back into the program. Even if I don’t use a real file, I can still use these techniques to send the data down a socket or in an email.

pack

The pack built-in takes data and turns it into a single string by using a template string to decide how to put the data together. It’s similar to sprintf, although like its name suggests, ...