1foreach(n) Tcl Built-In Commands foreach(n)
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8 foreach - Iterate over all elements in one or more lists
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11 foreach varname list body
12 foreach varlist1 list1 ?varlist2 list2 ...? body
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17 The foreach command implements a loop where the loop variable(s) take
18 on values from one or more lists. In the simplest case there is one
19 loop variable, varname, and one list, list, that is a list of values to
20 assign to varname. The body argument is a Tcl script. For each ele‐
21 ment of list (in order from first to last), foreach assigns the con‐
22 tents of the element to varname as if the lindex command had been used
23 to extract the element, then calls the Tcl interpreter to execute body.
24 In the general case there can be more than one value list (e.g., list1
26 and list2), and each value list can be associated with a list of loop
27 variables (e.g., varlist1 and varlist2). During each iteration of the
28 loop the variables of each varlist are assigned consecutive values from
29 the corresponding list. Values in each list are used in order from
30 first to last, and each value is used exactly once. The total number
31 of loop iterations is large enough to use up all the values from all
32 the value lists. If a value list does not contain enough elements for
33 each of its loop variables in each iteration, empty values are used for
34 the missing elements.
35 The break and continue statements may be invoked inside body, with the
37 same effect as in the for command. Foreach returns an empty string.
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40 This loop prints every value in a list together with the square and
41 cube of the value:
42 set values {1 3 5 7 2 4 6 8} ;# Odd numbers first, for fun!
44 puts "Value\tSquare\tCube" ;# Neat-looking header
45 foreach x $values { ;# Now loop and print...
46 puts " $x\t [expr {$x**2}]\t [expr {$x**3}]"
47 }
48 The following loop uses i and j as loop variables to iterate over pairs
50 of elements of a single list.
51 set x {}
53 foreach {i j} {a b c d e f} {
54 lappend x $j $i
55 }
56 # The value of x is "b a d c f e"
57 # There are 3 iterations of the loop.
58 The next loop uses i and j to iterate over two lists in parallel.
60 set x {}
62 foreach i {a b c} j {d e f g} {
63 lappend x $i $j
64 }
65 # The value of x is "a d b e c f {} g"
66 # There are 4 iterations of the loop.
67 The two forms are combined in the following example.
69 set x {}
71 foreach i {a b c} {j k} {d e f g} {
72 lappend x $i $j $k
73 }
74 # The value of x is "a d e b f g c {} {}"
75 # There are 3 iterations of the loop.
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79 for(n), while(n), break(n), continue(n)
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83 foreach, iteration, list, loop
84Tcl foreach(n)