Node:Expressions, Next:Patterns and Actions, Previous:Printing, Up:Top

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.

• Constants: String, numeric and regexp constants.
• Using Constant Regexps: When and how to use a regexp constant.
• Variables: Variables give names to values for later use.
• Conversion: The conversion of strings to numbers and vice versa.
• Arithmetic Ops: Arithmetic operations (+, -, etc.)
• Concatenation: Concatenating strings.
• Assignment Ops: Changing the value of a variable or a field.
• Increment Ops: Incrementing the numeric value of a variable.
• Truth Values: What is ``true'' and what is ``false''.
• Typing and Comparison: How variables acquire types and how this affects comparison of numbers and strings with <, etc.
• Boolean Ops: Combining comparison expressions using boolean operators || (``or''), && (``and'') and ! (``not'').
• Conditional Exp: Conditional expressions select between two subexpressions under control of a third subexpression.
• Function Calls: A function call is an expression.
• Precedence: How various operators nest.