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  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
       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)