1switch(n) Tcl Built-In Commands switch(n)
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8 switch - Evaluate one of several scripts, depending on a given value
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11 switch ?options? string pattern body ?pattern body ...?
12 switch ?options? string {pattern body ?pattern body ...?}
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18 The switch command matches its string argument against each of the pat‐
19 tern arguments in order. As soon as it finds a pattern that matches
20 string it evaluates the following body argument by passing it recur‐
21 sively to the Tcl interpreter and returns the result of that evalua‐
22 tion. If the last pattern argument is default then it matches any‐
23 thing. If no pattern argument matches string and no default is given,
24 then the switch command returns an empty string.
25 If the initial arguments to switch start with - then they are treated
27 as options. The following options are currently supported:
28 -exact Use exact matching when comparing string to a pattern. This
30 is the default.
31 -glob When matching string to the patterns, use glob-style matching
33 (i.e. the same as implemented by the string match command).
34 -regexp When matching string to the patterns, use regular expression
36 matching (as described in the re_syntax reference page).
37 -- Marks the end of options. The argument following this one
39 will be treated as string even if it starts with a -.
40 Two syntaxes are provided for the pattern and body arguments. The
42 first uses a separate argument for each of the patterns and commands;
43 this form is convenient if substitutions are desired on some of the
44 patterns or commands. The second form places all of the patterns and
45 commands together into a single argument; the argument must have proper
46 list structure, with the elements of the list being the patterns and
47 commands. The second form makes it easy to construct multi-line switch
48 commands, since the braces around the whole list make it unnecessary to
49 include a backslash at the end of each line. Since the pattern argu‐
50 ments are in braces in the second form, no command or variable substi‐
51 tutions are performed on them; this makes the behavior of the second
52 form different than the first form in some cases.
53 If a body is specified as ``-'' it means that the body for the next
55 pattern should also be used as the body for this pattern (if the next
56 pattern also has a body of ``-'' then the body after that is used, and
57 so on). This feature makes it possible to share a single body among
58 several patterns.
59 Beware of how you place comments in switch commands. Comments should
61 only be placed inside the execution body of one of the patterns, and
62 not intermingled with the patterns.
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65 The switch command can match against variables and not just literals,
66 as shown here (the result is 2):
67 set foo "abc"
68 switch abc a - b {expr 1} $foo {expr 2} default {expr 3}
69 Using glob matching and the fall-through body is an alternative to
71 writing regular expressions with alternations, as can be seen here
72 (this returns 1):
73 switch -glob aaab {
74 a*b -
75 b {expr 1}
76 a* {expr 2}
77 default {expr 3}
78 }
79 Whenever nothing matches, the default clause (which must be last) is
81 taken. This example has a result of 3:
82 switch xyz {
83 a -
84 b {
85 # Correct Comment Placement
86 expr 1
87 }
88 c {
89 expr 2
90 }
91 default {
92 expr 3
93 }
94 }
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98 for(n), if(n), regexp(n)
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102 switch, match, regular expression
103Tcl 7.0 switch(n)