Import Tcl-core 8.6.6 (as of svn r86089)

doc/while.n

@@ -0,0 +1,65 @@
+'\"
+'\" 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.
+'\"
+.TH while n "" Tcl "Tcl Built-In Commands"
+.so man.macros
+.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$x<10\fR:
+.PP
+.CS
+set x 0
+\fBwhile\fR {$x<10} {
+    puts "x is $x"
+    incr x
+}
+.CE
+.SH EXAMPLE
+.PP
+Read lines from a channel until we get to the end of the stream, and
+print them out with a line-number prepended:
+.PP
+.CS
+set lineCount 0
+\fBwhile\fR {[gets $chan line] >= 0} {
+    puts "[incr lineCount]: $line"
+}
+.CE
+.SH "SEE ALSO"
+break(n), continue(n), for(n), foreach(n)
+.SH KEYWORDS
+boolean, loop, test, while