switch (n)
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\0abc\0a\0-\0b\0{format 1}\0abc\0{format 2}\0default\0{format 3}
will return 2,
switch\0-regexp\0aaab {
^a.*b$\0-
b\0{format 1}
a*\0{format 2}
default\0{format 3}
}
will return 1, and
switch\0xyz {
a
-
b
{format 1}
a*
{format 2}
default
{format 3}
}
will return 3.
KEYWORDS
switch, match, regular expression
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