File: gawk.info,  Node: Switch Statement,  Next: Break Statement,  Prev: For Statement,  Up: Statements

7.4.5 The 'switch' Statement
----------------------------

This minor node describes a 'gawk'-specific feature.  If 'gawk' is in
compatibility mode (*note 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 (either regular, '/foo/', or strongly typed, '@/foo/')
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
*note Getopt Function::.)