NAME

       lset - Change an element in a list

SYNOPSIS

       lset varName ?index ...? newValue
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DESCRIPTION

       The  lset  command  accepts  a  parameter,  varName,  which it interprets as the name of a
       variable containing a Tcl list.  It also accepts zero or more indices into the list.   The
       indices  may  be  presented  either consecutively on the command line, or grouped in a Tcl
       list and presented as a single argument.  Finally, it accepts a new value for  an  element
       of varName.

       If no indices are presented, the command takes the form:

              lset varName newValue

       or

              lset varName {} newValue

       In this case, newValue replaces the old value of the variable varName.

       When  presented  with  a  single index, the lset command treats the content of the varName
       variable as a Tcl list.  It addresses the index'th element in it (0 refers  to  the  first
       element of the list).  When interpreting the list, lset observes the same rules concerning
       braces and quotes and backslashes  as  the  Tcl  command  interpreter;  however,  variable
       substitution  and command substitution do not occur.  The command constructs a new list in
       which the designated element is replaced with newValue.  This new list is  stored  in  the
       variable varName, and is also the return value from the lset command.

       If  index  is  negative  or greater than the number of elements in $varName, then an error
       occurs.

       If index is equal to the number of  elements  in  $varName,  then  the  given  element  is
       appended to the list.

       The interpretation of each simple index value is the same as for the command string index,
       supporting simple index arithmetic and indices relative to the end of the list.

       If additional index arguments are supplied, then each argument is used in turn to  address
       an  element  within  a sublist designated by the previous indexing operation, allowing the
       script to alter elements in sublists (or append elements to sublists).  The command,

              lset a 1 2 newValue

       or

              lset a {1 2} newValue

       replaces element 2 of sublist 1 with newValue.

       The integer appearing in each index argument must be greater than or equal to  zero.   The
       integer  appearing  in each index argument must be less than or equal to the length of the
       corresponding list.  In other words, the lset command can change the size of a  list  only
       by  appending  an element (setting the one after the current end).  If an index is outside
       the permitted range, an error is reported.

EXAMPLES

       In each of these examples, the initial value of x is:

              set x [list [list a b c] [list d e f] [list g h i]]
                    → {a b c} {d e f} {g h i}

       The indicated return value also becomes the new value of x (except in the last case, which
       is an error which leaves the value of x unchanged.)

              lset x {j k l}
                    → j k l
              lset x {} {j k l}
                    → j k l
              lset x 0 j
                    → j {d e f} {g h i}
              lset x 2 j
                    → {a b c} {d e f} j
              lset x end j
                    → {a b c} {d e f} j
              lset x end-1 j
                    → {a b c} j {g h i}
              lset x 2 1 j
                    → {a b c} {d e f} {g j i}
              lset x {2 1} j
                    → {a b c} {d e f} {g j i}
              lset x {2 3} j
                    → list index out of range

       In the following examples, the initial value of x is:

              set x [list [list [list a b] [list c d]] \
                          [list [list e f] [list g h]]]
                    → {{a b} {c d}} {{e f} {g h}}

       The indicated return value also becomes the new value of x.

              lset x 1 1 0 j
                    → {{a b} {c d}} {{e f} {j h}}
              lset x {1 1 0} j
                    → {{a b} {c d}} {{e f} {j h}}

SEE ALSO

       list(3tcl),  lappend(3tcl),  lindex(3tcl),  linsert(3tcl),  llength(3tcl),  lsearch(3tcl),
       lsort(3tcl), lrange(3tcl), lreplace(3tcl), string(3tcl)

KEYWORDS

       element, index, list, replace, set