| [25] | 1 | '\" |
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| 2 | '\" Copyright (c) 1993 The Regents of the University of California. |
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| 3 | '\" Copyright (c) 1994-1997 Sun Microsystems, Inc. |
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| 4 | '\" |
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| 5 | '\" See the file "license.terms" for information on usage and redistribution |
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| 6 | '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. |
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| 7 | '\" |
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| 8 | '\" RCS: @(#) $Id: while.n,v 1.5 2004/10/27 14:43:54 dkf Exp $ |
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| 9 | '\" |
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| 10 | .so man.macros |
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| 11 | .TH while n "" Tcl "Tcl Built-In Commands" |
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| 12 | .BS |
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| 13 | '\" Note: do not modify the .SH NAME line immediately below! |
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| 14 | .SH NAME |
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| 15 | while \- Execute script repeatedly as long as a condition is met |
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| 16 | .SH SYNOPSIS |
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| 17 | \fBwhile \fItest body\fR |
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| 18 | .BE |
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| 19 | |
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| 20 | .SH DESCRIPTION |
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| 21 | .PP |
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| 22 | The \fBwhile\fR command evaluates \fItest\fR as an expression |
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| 23 | (in the same way that \fBexpr\fR evaluates its argument). |
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| 24 | The value of the expression must a proper boolean |
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| 25 | value; if it is a true value |
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| 26 | then \fIbody\fR is executed by passing it to the Tcl interpreter. |
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| 27 | Once \fIbody\fR has been executed then \fItest\fR is evaluated |
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| 28 | again, and the process repeats until eventually \fItest\fR |
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| 29 | evaluates to a false boolean value. \fBContinue\fR |
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| 30 | commands may be executed inside \fIbody\fR to terminate the current |
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| 31 | iteration of the loop, and \fBbreak\fR |
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| 32 | commands may be executed inside \fIbody\fR to cause immediate |
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| 33 | termination of the \fBwhile\fR command. The \fBwhile\fR command |
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| 34 | always returns an empty string. |
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| 35 | .PP |
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| 36 | Note: \fItest\fR should almost always be enclosed in braces. If not, |
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| 37 | variable substitutions will be made before the \fBwhile\fR |
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| 38 | command starts executing, which means that variable changes |
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| 39 | made by the loop body will not be considered in the expression. |
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| 40 | This is likely to result in an infinite loop. If \fItest\fR is |
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| 41 | enclosed in braces, variable substitutions are delayed until the |
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| 42 | expression is evaluated (before |
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| 43 | each loop iteration), so changes in the variables will be visible. |
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| 44 | For an example, try the following script with and without the braces |
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| 45 | around \fB$x<10\fR: |
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| 46 | .CS |
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| 47 | set x 0 |
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| 48 | \fBwhile\fR {$x<10} { |
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| 49 | puts "x is $x" |
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| 50 | incr x |
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| 51 | } |
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| 52 | .CE |
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| 53 | .SH EXAMPLE |
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| 54 | Read lines from a channel until we get to the end of the stream, and |
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| 55 | print them out with a line-number prepended: |
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| 56 | .CS |
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| 57 | set lineCount 0 |
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| 58 | \fBwhile\fR {[gets $chan line] >= 0} { |
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| 59 | puts "[incr lineCount]: $line" |
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| 60 | } |
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| 61 | .CE |
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| 62 | |
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| 63 | .SH "SEE ALSO" |
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| 64 | break(n), continue(n), for(n), foreach(n) |
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| 65 | |
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| 66 | .SH KEYWORDS |
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| 67 | boolean value, loop, test, while |
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