while(3tcl) [debian man page]

while(3tcl)						       Tcl Built-In Commands						       while(3tcl)

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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 exe-
       cuted inside body to terminate the current iteration of the loop, and break commands may be executed inside body to cause immediate  termi-
       nation 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 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
       infinite loop.  If test is enclosed in braces, variable substitutions are delayed until the expression is evaluated (before each loop iter-
       ation), 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)

for(3tcl)						       Tcl Built-In Commands							 for(3tcl)

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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 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
       infinite loop.  If test is enclosed in braces, variable substitutions are delayed until the expression is evaluated (before each loop iter-
       ation), 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 10:
	      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, continue, foreach, while

KEYWORDS

       for, iteration, looping

Tcl																	 for(3tcl)