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lset(n)                                     Tcl Built-In Commands                                    lset(n)



____________________________________________________________________________________________________________

NAME
       lset - Change an element in a list

SYNOPSIS
       lset varName ?index...? newValue
____________________________________________________________________________________________________________

DESCRIPTION
       The lset command accepts a parameter, varName, which it interprets as the name of a variable contain-ing containing
       ing 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 argu-ment. argument.
       ment.  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 or equal to the number of elements in $varName, then an error
       occurs.

       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.  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 strictly less than the length of the corresponding list.  In
       other words, the lset command cannot change the size of a list.  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(n), lappend(n), lindex(n), linsert(n), llength(n), lsearch(n), lsort(n), lrange(n), lreplace(n), |
       string(n)



KEYWORDS
       element, index, list, replace, set



Tcl                                                  8.4                                             lset(n)