7.4.5 The switch Statement ¶

This section describes a gawk-specific feature. If gawk is in compatibility mode (see Command-Line 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 Processing Command-Line Options.)