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.so man.macros

.TH for n "" Tcl "Tcl Built-In Commands"

.BS

'\" Note:  do not modify the .SH NAME line immediately below!

.SH NAME

for \- ``For'' loop

.SH SYNOPSIS

\fBfor \fIstart test next body\fR

.BE

.SH DESCRIPTION

.PP

\fBFor\fR is a looping command, similar in structure to the C

\fBfor\fR statement.  The \fIstart\fR, \fInext\fR, and

\fIbody\fR arguments must be Tcl command strings, and \fItest\fR

is an expression string.

The \fBfor\fR command first invokes the Tcl interpreter to

execute \fIstart\fR.  Then it repeatedly evaluates \fItest\fR as

an expression; if the result is non-zero it invokes the Tcl

interpreter on \fIbody\fR, then invokes the Tcl interpreter on \fInext\fR,

then repeats the loop.  The command terminates when \fItest\fR evaluates

to 0.  If a \fBcontinue\fR command is invoked within \fIbody\fR then

any remaining commands in the current execution of \fIbody\fR are skipped;

processing continues by invoking the Tcl interpreter on \fInext\fR, then

evaluating \fItest\fR, and so on.  If a \fBbreak\fR command is invoked

within \fIbody\fR

or \fInext\fR,

then the \fBfor\fR command will

return immediately.

The operation of \fBbreak\fR and \fBcontinue\fR are similar to the

corresponding statements in C.

\fBFor\fR returns an empty string.

.PP

Note: \fItest\fR should almost always be enclosed in braces.  If not,

variable substitutions will be made before the \fBfor\fR

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 \fItest\fR 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.

For an example, try the following script with and without the braces

around \fB$x<10\fR:

.CS

for {set x 0} {$x<10} {incr x} {

        puts "x is $x"

}

.CE

.SH KEYWORDS

for, iteration, looping