foreach

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 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.  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.