man/mann/foreach.n

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'\" RCS: @(#) $Id: foreach.n,v 1.3 2000/09/07 14:27:48 poenitz Exp $
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'\" The definitions below are for supplemental macros used in Tcl/Tk
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.TH foreach n "" Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
foreach \- Iterate over all elements in one or more lists
.SH SYNOPSIS
\fBforeach \fIvarname list body\fR
.br
\fBforeach \fIvarlist1 list1\fR ?\fIvarlist2 list2 ...\fR? \fIbody\fR
.BE

.SH DESCRIPTION
.PP
The \fBforeach\fR command implements a loop where the loop
variable(s) take on values from one or more lists.
In the simplest case there is one loop variable, \fIvarname\fR,
and one list, \fIlist\fR, that is a list of values to assign to \fIvarname\fR.
The \fIbody\fR argument is a Tcl script.
For each element of \fIlist\fR (in order
from first to last), \fBforeach\fR assigns the contents of the
element to \fIvarname\fR as if the \fBlindex\fR command had been used
to extract the element, then calls the Tcl interpreter to execute
\fIbody\fR.
.PP
In the general case there can be more than one value list
(e.g., \fIlist1\fR and \fIlist2\fR),
and each value list can be associated with a list of loop variables
(e.g., \fIvarlist1\fR and \fIvarlist2\fR).
During each iteration of the loop
the variables of each \fIvarlist\fP are assigned
consecutive values from the corresponding \fIlist\fP.
Values in each \fIlist\fP are used in order from first to last,
and each value is used exactly once.
The total number of loop iterations is large enough to use
up all the values from all the value lists.
If a value list does not contain enough
elements for each of its loop variables in each iteration,
empty values are used for the missing elements.
.PP
The \fBbreak\fR and \fBcontinue\fR statements may be
invoked inside \fIbody\fR, with the same effect as in the \fBfor\fR
command.  \fBForeach\fR returns an empty string.
.SH EXAMPLES
.PP
The following loop uses i and j as loop variables to iterate over
pairs of elements of a single list.
.DS
set x {}
foreach {i j} {a b c d e f} {
    lappend x $j $i
}
# The value of x is "b a d c f e"
# There are 3 iterations of the loop.
.DE
.PP
The next loop uses i and j to iterate over two lists in parallel.
.DS
set x {}
foreach i {a b c} j {d e f g} {
    lappend x $i $j
}
# The value of x is "a d b e c f {} g"
# There are 4 iterations of the loop.
.DE
.PP
The two forms are combined in the following example.
.DS
set x {}
foreach i {a b c} {j k} {d e f g} {
    lappend x $i $j $k
}
# The value of x is "a d e b f g c {} {}"
# There are 3 iterations of the loop.
.DE

.SH "SEE ALSO"
for(n), while(n), break(n), continue(n)

.SH KEYWORDS
foreach, iteration, list, looping