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while(n)                                    Tcl Built-In Commands                                   while(n)



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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  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, variable substitutions will be made
       before the while 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 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-num-
       ber prepended:
              set lineCount 0
              while {[gets $chan line] >= 0} {
                  puts "[incr lineCount]: $line"
              }


SEE ALSO
       break(n), continue(n), for(n), foreach(n)


KEYWORDS
       boolean value, loop, test, while



Tcl                                                                                                 while(n)