foreach(n) Tcl Built-In Commands foreach(n)
NAME
foreach - 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 ele-
ment of list (in order from first to last), foreach assigns the con-
tents 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
This loop prints every value in a list together with the square and
cube of the value:
set values {1 3 5 7 2 4 6 8} ;# Odd numbers first, for fun! puts
"Value\tSquare\tCube" ;# Neat-looking header foreach x $values
{ ;# Now loop and print...
puts " $x\t [expr {$x**2}]\t [expr {$x**3}]" }
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, loop
Tcl foreach(n)
tcl 8.6.0 - Generated Wed Jan 9 06:24:59 CST 2013