(gawk.info) Expressions

 
 Expressions
 ***********
 
    Expressions are the basic building blocks of `awk' patterns and
 actions.  An expression evaluates to a value, which you can print, test,
 store in a variable or pass to a function.  Additionally, an expression
 can assign a new value to a variable or a field, with 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 which
 specify 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.

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