while(3tcl)						       Tcl Built-In Commands						       while(3tcl)

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NAME

       while - Execute script repeatedly as long as a condition is met

SYNOPSIS

       while test body
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DESCRIPTION

       The  while  command evaluates test as an expression (in the same way that expr evaluates its argument).	The value of the expression must a
       proper boolean value; if it is a true value then body is executed by passing it to the Tcl interpreter.	Once body has been  executed  then
       test  is  evaluated again, and the process repeats until eventually test evaluates to a false boolean value.  Continue commands may be exe-
       cuted inside body to terminate the current iteration of the loop, and break commands may be executed inside body to cause immediate  termi-
       nation of the while command.  The while command always returns an empty string.

       Note: test should almost always be enclosed in braces.  If not, variable substitutions will be made before the while command starts execut-
       ing, 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 test is enclosed in braces, variable substitutions are delayed until the expression is evaluated (before each loop iter-
       ation), so changes in the variables will be visible.  For an example, try the following script with and without the braces around $x<10:
	      set x 0
	      while {$x<10} {
		  puts "x is $x"
		  incr x
	      }

EXAMPLE

       Read lines from a channel until we get to the end of the stream, and print them out with a line-number prepended:
	      set lineCount 0
	      while {[gets $chan line] >= 0} {
		  puts "[incr lineCount]: $line"
	      }

SEE ALSO

       break(3tcl), continue(3tcl), for(3tcl), foreach(3tcl)

KEYWORDS

       boolean value, loop, test, while

Tcl																       while(3tcl)