tcl7.6 User Commands - switch
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 pat-
tern 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 follow-
ing this one will be treated as string even if it
starts with a -.
Two syntaxes are provided for the pattern and body argu-
ments. The first uses a separate argument for each of the
patterns and commands; this form is convenient if substitu-
tions 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