foreach(3tcl)

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

   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(3tcl), while(3tcl), break(3tcl), continue(3tcl)

KEYWORDS

   foreach, iteration, list, looping

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