switch(3Tcl)

NAME
     switch - Evaluate one of several scripts, depending on a given value

SYNOPSIS
     switch ?options? string pattern body ?pattern body ...?
     switch ?options? string {pattern body ?pattern body ...?}


DESCRIPTION
     The switch command matches its string argument against each of the
     pattern arguments in order.  As soon as it finds a pattern that matches
     string it evaluates the following body argument by passing it recursively
     to the Tcl interpreter and returns the result of that evaluation.  If the
     last pattern argument is default then it matches anything.  If no pattern
     argument matches string and no default is given, then the switch command
     returns an empty string.

     If the initial arguments to switch start with - then they are treated as
     options.  The following options are currently supported:

     -exact    Use exact matching when comparing string to a pattern.  This is
               the default.

     -glob     When matching string to the patterns, use glob-style matching
               (i.e. the same as implemented by the string match command).

     -regexp   When matching string to the patterns, use regular expression
               matching (i.e. the same as implemented by the regexp command).

     --        Marks the end of options.  The argument following this one will
               be treated as string even if it starts with a -.

     Two syntaxes are provided for the pattern and body arguments.  The first
     uses a separate argument for each of the patterns and commands; this form
     is convenient if substitutions are desired on some of the patterns or
     commands.  The second form places all of the patterns and commands
     together into a single argument; the argument must have proper list
     structure, with the elements of the list being the patterns and commands.
     The second form makes it easy to construct multi-line switch commands,
     since the braces around the whole list make it unnecessary to include a
     backslash at the end of each line.  Since the pattern arguments are in
     braces in the second form, no command or variable substitutions are
     performed on them;  this makes the behavior of the second form different
     than the first form in some cases.

     If a body is specified as ``-'' it means that the body for the next
     pattern should also be used as the body for this pattern (if the next
     pattern also has a body of ``-'' then the body after that is used, and so
     on).  This feature makes it possible to share a single body among several
     patterns.
     Below are some examples of switch commands:

          switch abc a - b {format 1} abc {format 2} default {format 3}

     will return 2,

          switch -regexp aaab {
            ^a.*b$ -
            b {format 1}
            a* {format 2}
            default {format 3}
          }

     will return 1, and

          switch xyz {
            a
              -
            b
              {format 1}
            a*
              {format 2}
            default
              {format 3}
          }

     will return 3.


KEYWORDS
     switch, match, regular expression