Perl Best Practices

Chapter 4. Values and Expressions

Data is semi-animate…sort of like programmers.

—Arthur Norman

Constructing and using values ought to be trivial. After all, there are very few components of a Perl program simpler than a character string or a number or a + operator.

Unfortunately, the syntax of Perl's literal values is so rich that there are plenty of ways to mess them up. Variables can interpolate unexpectedly, or fail to interpolate at all. Character escape codes and literal numbers can mysteriously appear in the wrong base. Delimiters can be just about anything you like.

And Perl's operators are even worse. Several of them are polymorphic: silently changing their behaviour depending on the type of argument they're applied to. Others are monomorphic: silently changing their arguments to fit their behaviour. Others are just plain inefficient in some usages.

This chapter suggests some appropriate coding habits that can help you avoid the pitfalls associated with creating values and manipulating them in expressions.

String Delimiters

Use interpolating string delimiters only for strings that actually interpolate.

Unexpectedly interpolating a variable in a character string is a common source of errors in Perl programs. So is unexpected non-interpolation. Fortunately, Perl provides two distinct types of strings that make it easy to specify exactly what you want.

If you're creating a literal character string and you definitely intend to interpolate one or more variables into it, use a double-quoted ...