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gawk: Expressions Summary

 6.7 Summary
    * Expressions are the basic elements of computation in programs.
      They are built from constants, variables, function calls, and
      combinations of the various kinds of values with operators.
    * 'awk' supplies three kinds of constants: numeric, string, and
      regexp.  'gawk' lets you specify numeric constants in octal and
      hexadecimal (bases 8 and 16) as well as decimal (base 10).  In
      certain contexts, a standalone regexp constant such as '/foo/' has
      the same meaning as '$0 ~ /foo/'.
    * Variables hold values between uses in computations.  A number of
      built-in variables provide information to your 'awk' program, and a
      number of others let you control how 'awk' behaves.
    * Numbers are automatically converted to strings, and strings to
      numbers, as needed by 'awk'.  Numeric values are converted as if
      they were formatted with 'sprintf()' using the format in 'CONVFMT'.
      Locales can influence the conversions.
    * 'awk' provides the usual arithmetic operators (addition,
      subtraction, multiplication, division, modulus), and unary plus and
      minus.  It also provides comparison operators, Boolean operators,
      an array membership testing operator, and regexp matching
      operators.  String concatenation is accomplished by placing two
      expressions next to each other; there is no explicit operator.  The
      three-operand '?:' operator provides an "if-else" test within
    * Assignment operators provide convenient shorthands for common
      arithmetic operations.
    * In 'awk', a value is considered to be true if it is nonzero _or_
      non-null.  Otherwise, the value is false.
    * A variable's type is set upon each assignment and may change over
      its lifetime.  The type determines how it behaves in comparisons
      (string or numeric).
    * Function calls return a value that may be used as part of a larger
      expression.  Expressions used to pass parameter values are fully
      evaluated before the function is called.  'awk' provides built-in
      and user-defined functions; this is described in ⇒Functions.
    * Operator precedence specifies the order in which operations are
      performed, unless explicitly overridden by parentheses.  'awk''s
      operator precedence is compatible with that of C.
    * Locales can affect the format of data as output by an 'awk'
      program, and occasionally the format for data read as input.
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