NAME
  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, 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
  % set i 0
  0
  
  % while {$i < 10} {
      puts "Hello"
      set i [expr $i + 1]
    }
  Hello
  Hello
  Hello
  Hello
  Hello
  Hello
  Hello
  Hello
  Hello
  Hello

SEE ALSO
  break continue for foreach