(gawk.info.gz) Precedence

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 Operator Precedence (How Operators Nest)
 ========================================
 
    "Operator precedence" determines how operators are grouped when
 different operators appear close by in one expression.  For example,
 `*' has higher precedence than `+'; thus, `a + b * c' means to multiply
 `b' and `c', and then add `a' to the product (i.e., `a + (b * c)').
 
    The normal precedence of the operators can be overruled by using
 parentheses.  Think of the precedence rules as saying where the
 parentheses are assumed to be.  In fact, it is wise to always use
 parentheses whenever there is an unusual combination of operators,
 because other people who read the program may not remember what the
 precedence is in this case.  Even experienced programmers occasionally
 forget the exact rules, which leads to mistakes.  Explicit parentheses
 help prevent any such mistakes.
 
    When operators of equal precedence are used together, the leftmost
 operator groups first, except for the assignment, conditional, and
 exponentiation operators, which group in the opposite order.  Thus, `a
 - b + c' groups as `(a - b) + c' and `a = b = c' groups as `a = (b =
 c)'.
 
    The precedence of prefix unary operators does not matter as long as
 only unary operators are involved, because there is only one way to
 interpret them: innermost first.  Thus, `$++i' means `$(++i)' and
 `++$x' means `++($x)'.  However, when another operator follows the
 operand, then the precedence of the unary operators can matter.  `$x^2'
 means `($x)^2', but `-x^2' means `-(x^2)', because `-' has lower
 precedence than `^', whereas `$' has higher precedence.  This table
 presents `awk''s operators, in order of highest to lowest precedence:
 
 `(...)'
      Grouping.
 
 `$'
      Field.
 
 `++ --'
      Increment, decrement.
 
 `^ **'
      Exponentiation.  These operators group right-to-left.
 
 `+ - !'
      Unary plus, minus, logical "not."
 
 `* / %'
      Multiplication, division, modulus.
 
 `+ -'
      Addition, subtraction.
 
 `String Concatenation'
      No special symbol is used to indicate concatenation.  The operands
      are simply written side by side ( String Concatenation
      Concatenation.).
 
 `< <= == !='
 `> >= >> | |&'
      Relational and redirection.  The relational operators and the
      redirections have the same precedence level.  Characters such as
      `>' serve both as relationals and as redirections; the context
      distinguishes between the two meanings.
 
      Note that the I/O redirection operators in `print' and `printf'
      statements belong to the statement level, not to expressions.  The
      redirection does not produce an expression that could be the
      operand of another operator.  As a result, it does not make sense
      to use a redirection operator near another operator of lower
      precedence without parentheses.  Such combinations (for example,
      `print foo > a ? b : c'), result in syntax errors.  The correct
      way to write this statement is `print foo > (a ? b : c)'.
 
 `~ !~'
      Matching, nonmatching.
 
 `in'
      Array membership.
 
 `&&'
      Logical "and".
 
 `||'
      Logical "or".
 
 `?:'
      Conditional.  This operator groups right-to-left.
 
 `= += -= *='
 `/= %= ^= **='
      Assignment.  These operators group right to left.
 
    (gawk.info.gz)`**' `**', and `**=' operators are not specified by
 POSIX.  For maximum portability, do not use them.
 

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