Expressions
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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.