6. 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.

6.1 Constant Expressions		String, numeric and regexp constants.
6.2 Using Regular Expression Constants		When and how to use a regexp constant.
6.3 Variables		Variables give names to values for later use.
6.4 Conversion of Strings and Numbers		The conversion of strings to numbers and vice versa.
6.5 Arithmetic Operators		Arithmetic operations (`+', `-', etc.)
6.6 String Concatenation		Concatenating strings.
6.7 Assignment Expressions		Changing the value of a variable or a field.
6.8 Increment and Decrement Operators		Incrementing the numeric value of a variable.
6.9 True and False in awk		What is "true" and what is "false".
6.10 Variable Typing and Comparison Expressions		How variables acquire types and how this affects comparison of numbers and strings with

                                `<', etc.

6.11 Boolean Expressions

Combining comparison expressions using boolean operators `||' ("or"), `&&'

                                ("and") and `!' ("not").

6.12 Conditional Expressions		Conditional expressions select between two subexpressions under control of a third subexpression.
6.13 Function Calls		A function call is an expression.
6.14 Operator Precedence (How Operators Nest)		How various operators nest.