lset man page on OpenDarwin

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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 containing a Tcl list.  It also accepts zero  or
       more  indices  into the list.  The indices may be presented either con‐
       secutively 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 varBane variable as a Tcl list.	It addresses the index'th ele‐
       ment in it (0 refers to the first element of the	 list).	  When	inter‐
       preting	the  list,  lset observes the same rules concerning braces and
       quotes and backslashes as the Tcl command interpreter;  however,	 vari‐
       able  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.

       If  index has the value end, it refers to the last element in the list,
       and end-integer refers to the last element in the list minus the speci‐
       fied integer offset.

       If  additional index arguments are supplied, then each argument is used
       in turn to address an element within a sublist designated by the previ‐
       ous  indexing  operation, allowing the script to alter elements in sub‐
       lists.  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)

KEYWORDS
       element, index, list, replace, set

Tcl				      8.4			       lset(n)
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