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'\"

'\" 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.

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'\" RCS: @(#) $Id: while.n,v 1.1.1.1 2002-01-16 10:25:25 markom Exp $

'\"

.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