NAME

       for - 'For' loop

SYNOPSIS

       for start test next body
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DESCRIPTION

       For  is  a looping command, similar in structure to the C for statement.  The start, next,
       and body arguments must be Tcl command strings, and test is an expression string.  The for
       command  first invokes the Tcl interpreter to execute start.  Then it repeatedly evaluates
       test as an expression; if the result is non-zero it invokes the Tcl interpreter  on  body,
       then  invokes  the Tcl interpreter on next, then repeats the loop.  The command terminates
       when test evaluates to 0.  If a continue command is invoked within body then any remaining
       commands  in  the  current execution of body are skipped; processing continues by invoking
       the Tcl interpreter on next, then evaluating test, and so  on.   If  a  break  command  is
       invoked  within body or next, then the for command will return immediately.  The operation
       of break and continue are similar to the corresponding statements in C.   For  returns  an
       empty string.

       Note:  test  should  almost  always be enclosed in braces.  If not, variable substitutions
       will be made before the for 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.  See below for an example:

EXAMPLES

       Print a line for each of the integers from 0 to 9:

              for {set x 0} {$x<10} {incr x} {
                  puts "x is $x"
              }

       Either loop infinitely or not at all because the expression being  evaluated  is  actually
       the  constant, or even generate an error!  The actual behaviour will depend on whether the
       variable x exists before the for command is run and whether its value is a value  that  is
       less  than  or  greater  than/equal  to  ten,  and  this is because the expression will be
       substituted before the for command is executed.

              for {set x 0} $x<10 {incr x} {
                  puts "x is $x"
              }

       Print out the powers of two from 1 to 1024:

              for {set x 1} {$x<=1024} {set x [expr {$x * 2}]} {
                  puts "x is $x"
              }

SEE ALSO

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

KEYWORDS

       boolean, for, iteration, loop