foreach(n) Tcl 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
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
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foreach(n) Tcl foreach(n)
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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