NAME
foreach - Iterate over all elements in one or more lists
SYNOPSIS
foreach varname list body
foreach varlist1 list1 ?varlist2 list2 ...? body
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DESCRIPTION
The foreach command implements a loop where the loop vari
able(s) take on values from one or more lists. In the
simplest case there is one loop variable, varname, and one
list, list, that is a list of values to assign to varname.
The body argument is a Tcl script. For each element of
list (in order from first to last), foreach assigns the
contents of the element to varname as if the lindex com
mand had been used to extract the element, then calls the
Tcl interpreter to execute body.
In the general case there can be more than one value list
(e.g., list1 and list2), and each value list can be asso
ciated with a list of loop variables (e.g., varlist1 and
varlist2). During each iteration of the loop the vari
ables of each varlist are assigned consecutive values from
the corresponding list. Values in each list 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.
The break and continue statements may be invoked inside
body, with the same effect as in the for command. Foreach
returns an empty string.
EXAMPLES
The following loop uses i and j as loop variables to iter
ate over pairs of elements of a single list.
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.
The next loop uses i and j to iterate over two lists in
parallel.
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.
The two forms are combined in the following example.
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.
SEE ALSO
for(n), while(n), break(n), continue(n)
KEYWORDS
foreach, iteration, list, looping
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