switch(n) Tcl (7.0) switch(n)
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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 (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
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switch(n) Tcl (7.0) switch(n)
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
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