(gawk.info.gz) Expressions

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 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.
 

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* 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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