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'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\" Copyright (c) 2001 by Kevin B. Kenny <kennykb@acm.org>. All rights reserved.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
'\" RCS: @(#) $Id: lindex.n,v 1.21 2008/10/17 10:22:25 dkf Exp $
'\"
.so man.macros
.TH lindex n 8.4 Tcl "Tcl Built-In Commands"
.BS
'\" Note: do not modify the .SH NAME line immediately below!
.SH NAME
lindex \- Retrieve an element from a list
.SH SYNOPSIS
\fBlindex \fIlist ?index ...?\fR
.BE
.SH DESCRIPTION
.PP
The \fBlindex\fR command accepts a parameter, \fIlist\fR, which
it treats as a Tcl list. It also accepts zero or more \fIindices\fR 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.
.PP
If no indices are presented, the command takes the form:
.PP
.CS
lindex list
.CE
.PP
or
.PP
.CS
lindex list {}
.CE
.PP
In this case, the return value of \fBlindex\fR is simply the value of the
\fIlist\fR parameter.
.PP
When presented with a single index, the \fBlindex\fR command
treats \fIlist\fR as a Tcl list and returns the
\fIindex\fR'th element from it (0 refers to the first element of the list).
In extracting the element, \fBlindex\fR observes the same rules
concerning braces and quotes and backslashes as the Tcl command
interpreter; however, variable
substitution and command substitution do not occur.
If \fIindex\fR is negative or greater than or equal to the number
of elements in \fIvalue\fR, then an empty
string is returned.
The interpretation of each simple \fIindex\fR value is the same as
for the command \fBstring index\fR, supporting simple index
arithmetic and indices relative to the end of the list.
.PP
If additional \fIindex\fR arguments are supplied, then each argument is
used in turn to select an element from the previous indexing operation,
allowing the script to select elements from sublists. The command,
.PP
.CS
lindex $a 1 2 3
.CE
.PP
or
.PP
.CS
lindex $a {1 2 3}
.CE
.PP
is synonymous with
.PP
.CS
lindex [lindex [lindex $a 1] 2] 3
.CE
.SH EXAMPLES
.PP
Lists can be indexed into from either end:
.PP
.CS
\fBlindex\fR {a b c} 0
\fI\(-> a\fR
\fBlindex\fR {a b c} 2
\fI\(-> c\fR
\fBlindex\fR {a b c} end
\fI\(-> c\fR
\fBlindex\fR {a b c} end-1
\fI\(-> b\fR
.CE
.PP
Lists or sequences of indices allow selection into lists of lists:
.PP
.CS
\fBlindex\fR {a b c}
\fI\(-> a b c\fR
\fBlindex\fR {a b c} {}
\fI\(-> a b c\fR
\fBlindex\fR {{a b c} {d e f} {g h i}} 2 1
\fI\(-> h\fR
\fBlindex\fR {{a b c} {d e f} {g h i}} {2 1}
\fI\(-> h\fR
\fBlindex\fR {{{a b} {c d}} {{e f} {g h}}} 1 1 0
\fI\(-> g\fR
\fBlindex\fR {{{a b} {c d}} {{e f} {g h}}} {1 1 0}
\fI\(-> g\fR
.CE
.PP
List indices may also perform limited computation, adding or subtracting fixed
amounts from other indices:
.PP
.CS
set idx 1
\fBlindex\fR {a b c d e f} $idx+2
\fI\(-> d\fR
set idx 3
\fBlindex\fR {a b c d e f} $idx+2
\fI\(-> f\fR
.CE
.SH "SEE ALSO"
list(n), lappend(n), linsert(n), llength(n), lsearch(n),
lset(n), lsort(n), lrange(n), lreplace(n),
string(n)
.SH KEYWORDS
element, index, list
'\"Local Variables:
'\"mode: nroff
'\"End:
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