1while(n) Tcl Built-In Commands while(n)
2______________________________________________________________________________
6
8 while - Execute script repeatedly as long as a condition is met
9
11 while test body
12______________________________________________________________________________
13
15 The while command evaluates test as an expression (in the same way that
16 expr evaluates its argument). The value of the expression must a
17 proper boolean value; if it is a true value then body is executed by
18 passing it to the Tcl interpreter. Once body has been executed then
19 test is evaluated again, and the process repeats until eventually test
20 evaluates to a false boolean value. Continue commands may be executed
21 inside body to terminate the current iteration of the loop, and break
22 commands may be executed inside body to cause immediate termination of
23 the while command. The while command always returns an empty string.
24 Note: test should almost always be enclosed in braces. If not, vari‐
26 able substitutions will be made before the while command starts execut‐
27 ing, which means that variable changes made by the loop body will not
28 be considered in the expression. This is likely to result in an infi‐
29 nite loop. If test is enclosed in braces, variable substitutions are
30 delayed until the expression is evaluated (before each loop iteration),
31 so changes in the variables will be visible. For an example, try the
32 following script with and without the braces around $x<10:
33 set x 0
35 while {$x<10} {
36 puts "x is $x"
37 incr x
38 }
39
41 Read lines from a channel until we get to the end of the stream, and
42 print them out with a line-number prepended:
43 set lineCount 0
45 while {[gets $chan line] >= 0} {
46 puts "[incr lineCount]: $line"
47 }
48
50 break(n), continue(n), for(n), foreach(n)
51
53 boolean, loop, test, while
54Tcl while(n)