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 exe
cute 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 immedi
ately. 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 substitu
tions 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 $x<10:
for {set x 0} {$x<10} {incr x} {
puts "x is $x"
}
SEE ALSO
break, continue, foreach, while
KEYWORDS
for, iteration, looping
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