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 fol
lowing 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 any
thing. 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 cur
rently 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 regu
lar expression matching (as described in the
re_syntax reference page).
-- 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 substi
tutions 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
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. Com
ments should only be placed inside the execution body of
one of the patterns, and not intermingled with the pat
terns.
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
{
# Correct Comment Placement
format 1
}
a*
{format 2}
default
{format 3}
}
will return 3.
SEE ALSO
for(n), if(n), regexp(n)
KEYWORDS
switch, match, regular expression
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