Effective awk Programming, 3rd Edition

Chapter 5. Expressions

Expressions are the basic building blocks of awk patterns and actions. An expression evaluates to a value that you can print, test, or pass to a function. Additionally, an expression can assign a new value to a variable or a field by using an assignment operator.

An expression can serve as a pattern or action statement on its own. Most other kinds of statements contain one or more expressions that specify the data on which to operate. As in other languages, expressions in awk include variables, array references, constants, and function calls, as well as combinations of these with various operators.

Constant Expressions

The simplest type of expression is the constant, which always has the same value. There are three types of constants: numeric, string, and regular expression.

Each is used in the appropriate context when you need a data value that isn’t going to change. Numeric constants can have different forms, but are stored identically internally.

Numeric and String Constants

A numeric constant stands for a number. This number can be an integer, a decimal fraction, or a number in scientific (exponential) notation.^[1] Here are some examples of numeric constants that all have the same value:

105
1.05e+2
1050e-1

A string constant consists of a sequence of characters enclosed in double-quotation marks. For example:

"parrot"

represents the string whose contents are parrot. Strings in gawk can be of any length, and they can contain any of the possible ...