for — 'For' loop
for start test next body
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 that 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:
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"
}
break, continue, foreach, while
boolean, for, iteration, loop
Copyright © 1993 The Regents of the University of California.
Copyright © 1994-1997 Sun Microsystems, Inc.