Perl Cookbook, 2nd Edition

Chapter 2. Numbers

Anyone who considers arithmetical methods of producing random digits is, of course, in a state of sin.

—John von Neumann (1951)

Introduction

Numbers, the most basic data type of almost any programming language, can be surprisingly tricky. Random numbers, numbers with decimal points, series of numbers, and conversion between strings and numbers all pose trouble.

Perl works hard to make life easy for you, and the facilities it provides for manipulating numbers are no exception to that rule. If you treat a scalar value as a number, Perl converts it to one. This means that when you read ages from a file, extract digits from a string, or acquire numbers from any of the other myriad textual sources that Real Life pushes your way, you don’t need to jump through the hoops created by other languages’ cumbersome requirements to turn an ASCII string into a number.

Perl tries its best to interpret a string as a number when you use it as one (such as in a mathematical expression), but it has no direct way of reporting that a string doesn’t represent a valid number. Perl quietly converts non-numeric strings to zero, and it will stop converting the string once it reaches a non-numeric character—so "A7" is still 0, and "7A" is just 7. (Note, however, that the -w flag will warn of such improper conversions.) Sometimes, such as when validating input, you need to know whether a string represents a valid number. We show you how in Recipe 2.1.

Recipe 2.15 shows how to get a number from ...