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gawk: Conditional Exp

 
 6.3.4 Conditional Expressions
 -----------------------------
 
 A "conditional expression" is a special kind of expression that has
 three operands.  It allows you to use one expression's value to select
 one of two other expressions.  The conditional expression in 'awk' is
 the same as in the C language, as shown here:
 
      SELECTOR ? IF-TRUE-EXP : IF-FALSE-EXP
 
 There are three subexpressions.  The first, SELECTOR, is always computed
 first.  If it is "true" (not zero or not null), then IF-TRUE-EXP is
 computed next, and its value becomes the value of the whole expression.
 Otherwise, IF-FALSE-EXP is computed next, and its value becomes the
 value of the whole expression.  For example, the following expression
 produces the absolute value of 'x':
 
      x >= 0 ? x : -x
 
    Each time the conditional expression is computed, only one of
 IF-TRUE-EXP and IF-FALSE-EXP is used; the other is ignored.  This is
 important when the expressions have side effects.  For example, this
 conditional expression examines element 'i' of either array 'a' or array
 'b', and increments 'i':
 
      x == y ? a[i++] : b[i++]
 
 This is guaranteed to increment 'i' exactly once, because each time only
 one of the two increment expressions is executed and the other is not.
 ⇒Arrays, for more information about arrays.
 
    As a minor 'gawk' extension, a statement that uses '?:' can be
 continued simply by putting a newline after either character.  However,
 putting a newline in front of either character does not work without
 using backslash continuation (⇒Statements/Lines).  If '--posix'
 is specified (⇒Options), this extension is disabled.
 
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