trusty (3) switch.3tcl.gz

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 ...?}
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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