foreach (n)
Iterate over all elements in one or more lists
SYNOPSIS
foreach varname list body
foreach varlist1 list1 ?varlist2 list2 ...? body
DESCRIPTION
The foreach 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, 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 command 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 associated with a list of loop variables
(e.g., varlist1 and varlist2).
During each iteration of the loop
the variables 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 iterate 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.
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.
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.
KEYWORDS
foreach, iteration, list, looping
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