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gawk: Switch Statement

 
 7.4.5 The 'switch' Statement
 ----------------------------
 
 This minor node describes a 'gawk'-specific feature.  If 'gawk' is in
 compatibility mode (Options), it is not available.
 
    The 'switch' statement allows the evaluation of an expression and the
 execution of statements based on a 'case' match.  Case statements are
 checked for a match in the order they are defined.  If no suitable
 'case' is found, the 'default' section is executed, if supplied.
 
    Each 'case' contains a single constant, be it numeric, string, or
 regexp.  The 'switch' expression is evaluated, and then each 'case''s
 constant is compared against the result in turn.  The type of constant
 determines the comparison: numeric or string do the usual comparisons.
 A regexp constant does a regular expression match against the string
 value of the original expression.  The general form of the 'switch'
 statement looks like this:
 
      switch (EXPRESSION) {
      case VALUE OR REGULAR EXPRESSION:
          CASE-BODY
      default:
          DEFAULT-BODY
      }
 
    Control flow in the 'switch' statement works as it does in C. Once a
 match to a given case is made, the case statement bodies execute until a
 'break', 'continue', 'next', 'nextfile', or 'exit' is encountered, or
 the end of the 'switch' statement itself.  For example:
 
      while ((c = getopt(ARGC, ARGV, "aksx")) != -1) {
          switch (c) {
          case "a":
              # report size of all files
              all_files = TRUE;
              break
          case "k":
              BLOCK_SIZE = 1024       # 1K block size
              break
          case "s":
              # do sums only
              sum_only = TRUE
              break
          case "x":
              # don't cross filesystems
              fts_flags = or(fts_flags, FTS_XDEV)
              break
          case "?":
          default:
              usage()
              break
          }
      }
 
    Note that if none of the statements specified here halt execution of
 a matched 'case' statement, execution falls through to the next 'case'
 until execution halts.  In this example, the 'case' for '"?"' falls
 through to the 'default' case, which is to call a function named
 'usage()'.  (The 'getopt()' function being called here is described in
 Getopt Function.)
 

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