switch(3Tcl) switch(3Tcl)
switch - Evaluate one of several scripts, depending on a given value
switch ?options? string pattern body ?pattern body ...?
switch ?options? string {pattern body ?pattern body ...?}
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.
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switch(3Tcl) switch(3Tcl)
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.
switch, match, regular expression
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