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author | rjohnson <rjohnson> | 1998-03-26 14:45:59 (GMT) |
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committer | rjohnson <rjohnson> | 1998-03-26 14:45:59 (GMT) |
commit | 2b5738da524e944cda39e24c0a87b745a43bd8c3 (patch) | |
tree | 6e8c9473978f6dab66c601e911721a7bd9d70b1b /doc/while.n | |
parent | c6a259aeeca4814a97cf6694814c63e74e4e18fa (diff) | |
download | tcl-2b5738da524e944cda39e24c0a87b745a43bd8c3.zip tcl-2b5738da524e944cda39e24c0a87b745a43bd8c3.tar.gz tcl-2b5738da524e944cda39e24c0a87b745a43bd8c3.tar.bz2 |
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diff --git a/doc/while.n b/doc/while.n new file mode 100644 index 0000000..326d18f --- /dev/null +++ b/doc/while.n @@ -0,0 +1,55 @@ +'\" +'\" Copyright (c) 1993 The Regents of the University of California. +'\" Copyright (c) 1994-1997 Sun Microsystems, Inc. +'\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +'\" SCCS: @(#) while.n 1.7 97/04/08 17:13:50 +'\" +.so man.macros +.TH while n "" Tcl "Tcl Built-In Commands" +.BS +'\" Note: do not modify the .SH NAME line immediately below! +.SH NAME +while \- Execute script repeatedly as long as a condition is met +.SH SYNOPSIS +\fBwhile \fItest body\fR +.BE + +.SH DESCRIPTION +.PP +The \fBwhile\fR command evaluates \fItest\fR as an expression +(in the same way that \fBexpr\fR evaluates its argument). +The value of the expression must a proper boolean +value; if it is a true value +then \fIbody\fR is executed by passing it to the Tcl interpreter. +Once \fIbody\fR has been executed then \fItest\fR is evaluated +again, and the process repeats until eventually \fItest\fR +evaluates to a false boolean value. \fBContinue\fR +commands may be executed inside \fIbody\fR to terminate the current +iteration of the loop, and \fBbreak\fR +commands may be executed inside \fIbody\fR to cause immediate +termination of the \fBwhile\fR command. The \fBwhile\fR command +always returns an empty string. +.PP +Note: \fItest\fR should almost always be enclosed in braces. If not, +variable substitutions will be made before the \fBwhile\fR +command starts executing, which means that variable changes +made by the loop body will not be considered in the expression. +This is likely to result in an infinite loop. If \fItest\fR is +enclosed in braces, variable substitutions are delayed until the +expression is evaluated (before +each loop iteration), so changes in the variables will be visible. +For an example, try the following script with and without the braces +around \fB$x<10\fR: +.CS +set x 0 +while {$x<10} { + puts "x is $x" + incr x +} +.CE + +.SH KEYWORDS +boolean value, loop, test, while |