switch(n) Tcl Built-In Commands 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 (as described in the
re_syntax reference page).
-- 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 substitu-tions substitutions
tions 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. Comments should only be placed inside the exe-cution execution
cution body of one of the patterns, and not intermingled with the 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 ^a.*b$b
b {format 1}
a* {format 2}
default {format 3}
}
will return 1, and
switch xyz {
a
-b ab
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
Tcl 7.0 switch(n)
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