Programming Perl, 4th Edition

Scalar Values

Whether it’s named directly or indirectly, and whether it’s in a variable, or an array element, or is just a temporary value, a scalar always contains a single value. This value may be a number, a string, or a reference to another piece of data. Or, there might even be no value at all, in which case the scalar is said to be undefined. Although we might speak of a scalar as “containing” a number or a string, scalars are typeless: you are not required to declare your scalars to be of type integer or floating point or string or whatever.

Future versions of Perl might allow you to insert int, num, and str type declarations. This is not to enforce strong typing, but to give the optimizer hints about things that it might not figure out for itself. Some CPAN modules already do this for you.

Perl stores strings as sequences of characters, with no arbitrary constraints on length or content. In human terms, you don’t have to decide in advance how long your strings are going to get, and you can include any characters, including null bytes, within your string. Perl stores numbers as signed (or unsigned) integers if possible, or as double-precision floating-point values in the machine’s native format otherwise. Floating-point values are not infinitely precise. This is important to remember because comparisons like (10/3 == 1/3*10) tend to fail mysteriously.

However, you can swap out Perl’s normal notions of numbers using the bigint, bigrat, and bignum pragmas. These provide integers, ...