foreach

foreach(3tcl)                Tcl Built-In Commands               foreach(3tcl)



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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 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, loop



Tcl                                                              foreach(3tcl)