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    Command:

    while

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

    SYNOPSIS

           while test body
    
    

    _________________________________________________________________

    
    
    

    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  executed
           inside  body  to terminate the current iteration of the loop, and break
           commands may be executed inside body to cause immediate termination  of
           the while command.  The while command always returns an empty string.
    
           Note:  test  should almost always be enclosed in braces.  If not, vari-
           able 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  infi-
           nite  loop.   If test 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 $x<10:
                  set x 0
                  while {$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)

    
    
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