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  (as
                 described in the re_syntax reference page).

       --        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.

       Beware of how you place comments in switch  commands.   Comments  should  only  be  placed
       inside the execution body of one of the patterns, and not intermingled with the patterns.

EXAMPLES

       The  switch  command can match against variables and not just literals, as shown here (the
       result is 2):
              set foo "abc"
              switch abc a - b {expr 1} $foo {expr 2} default {expr 3}

       Using glob matching and the  fall-through  body  is  an  alternative  to  writing  regular
       expressions with alternations, as can be seen here (this returns 1):
              switch -glob aaab {
                 a*b     -
                 b       {expr 1}
                 a*      {expr 2}
                 default {expr 3}
              }

       Whenever  nothing matches, the default clause (which must be last) is taken.  This example
       has a result of 3:
              switch xyz {
                 a  -
                 b {
                    # Correct Comment Placement
                    expr 1
                 }
                 c {
                    expr 2
                 }
                 default {
                    expr 3
                 }
              }

SEE ALSO

       for(3tcl), if(3tcl), regexp(3tcl)

KEYWORDS

       switch, match, regular expression