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gawk: If Statement

 
 7.4.1 The 'if'-'else' Statement
 -------------------------------
 
 The 'if'-'else' statement is 'awk''s decision-making statement.  It
 looks like this:
 
      'if (CONDITION) THEN-BODY' ['else ELSE-BODY']
 
 The CONDITION is an expression that controls what the rest of the
 statement does.  If the CONDITION is true, THEN-BODY is executed;
 otherwise, ELSE-BODY is executed.  The 'else' part of the statement is
 optional.  The condition is considered false if its value is zero or the
 null string; otherwise, the condition is true.  Refer to the following:
 
      if (x % 2 == 0)
          print "x is even"
      else
          print "x is odd"
 
    In this example, if the expression 'x % 2 == 0' is true (i.e., if the
 value of 'x' is evenly divisible by two), then the first 'print'
 statement is executed; otherwise, the second 'print' statement is
 executed.  If the 'else' keyword appears on the same line as THEN-BODY
 and THEN-BODY is not a compound statement (i.e., not surrounded by
 braces), then a semicolon must separate THEN-BODY from the 'else'.  To
 illustrate this, the previous example can be rewritten as:
 
      if (x % 2 == 0) print "x is even"; else
              print "x is odd"
 
 If the ';' is left out, 'awk' can't interpret the statement and it
 produces a syntax error.  Don't actually write programs this way,
 because a human reader might fail to see the 'else' if it is not the
 first thing on its line.
 
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