Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
for(n)			     Tcl Built-In Commands			for(n)

______________________________________________________________________________

NAME
       for - 'For' loop

SYNOPSIS
       for start test next body
______________________________________________________________________________

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  exe-
       cution  of  body	 are skipped; processing continues by invoking the Tcl
       interpreter on next, then evaluating test, and so on.  If a break  com-
       mand  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, vari-
       able substitutions will be made before the for 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.  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 eval-
       uated 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(n), continue(n), foreach(n), while(n)

KEYWORDS
       boolean,	for, iteration,	loop

Tcl									for(n)

NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | SEE ALSO | KEYWORDS

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=for.tcl86&manpath=FreeBSD+12.1-RELEASE+and+Ports>

home | help