Perl Cookbook

Chapter 8. File Contents

Introduction

The most brilliant decision in all of Unix was the choice of a single character for the newline sequence.

—Mike O’Dell, only half jokingly

Before the Unix Revolution, every kind of data source and destination was inherently different. Getting two programs merely to understand each other required heavy wizardry and the occasional sacrifice of a virgin stack of punch cards to an itinerant mainframe repairman. This computational Tower of Babel made programmers dream of quitting the field to take up a less painful hobby, like autoflagellation.

These days, such cruel and unusual programming is largely behind us. Modern operating systems work hard to provide the illusion that I/O devices, network connections, process control information, other programs, the system console, and even users’ terminals are all abstract streams of bytes called files. This lets you easily write programs that don’t care where their input came from or where their output goes.

Because programs read and write via byte streams of simple text, every program can communicate with every other program. It is difficult to overstate the power and elegance of this approach. No longer dependent upon troglodyte gnomes with secret tomes of JCL (or COM) incantations, users can now create custom tools from smaller ones by using simple command-line I/O redirection, pipelines, and backticks.

Treating files as unstructured byte streams necessarily governs what you can do with them. You can read ...