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Expressions as Action Statements

   Expressions are the basic building block of `awk' actions.  An
expression evaluates to a value, which you can print, test, store in a
variable or pass to a function.  But beyond that, an expression can
assign a new value to a variable or a field, with an assignment

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


String, numeric, and regexp constants.
Variables give names to values for later use.
Arithmetic Ops
Arithmetic operations (`+', `-', etc.)
Concatenating strings.
Comparison Ops
Comparison of numbers and strings with `<', etc.
Boolean Ops
Combining comparison expressions using boolean operators `||' ("or"), `&&' ("and") and `!' ("not").
Assignment Ops
Changing the value of a variable or a field.
Increment Ops
Incrementing the numeric value of a variable.
The conversion of strings to numbers and vice versa.
The whole truth about numbers and strings.
Conditional Exp
Conditional expressions select between two subexpressions under control of a third subexpression.
Function Calls
A function call is an expression.
How various operators nest.