foreach(n) Tcl Built-In Commands foreach(n)
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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 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 corre-sponding corresponding
sponding 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 com-mand. command.
mand. 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.
SEE ALSO
for(n), while(n), break(n), continue(n)
KEYWORDS
foreach, iteration, list, looping
Tcl foreach(n)
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