'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\" Copyright (c) 2001 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.
'\"
.TH lindex n 8.4 Tcl "Tcl Built-In Commands"
.\" The -*- nroff -*- definitions below are for supplemental macros used
.\" in Tcl/Tk manual entries.
.\"
.\" .AP type name in/out ?indent?
.\"	Start paragraph describing an argument to a library procedure.
.\"	type is type of argument (int, etc.), in/out is either "in", "out",
.\"	or "in/out" to describe whether procedure reads or modifies arg,
.\"	and indent is equivalent to second arg of .IP (shouldn't ever be
.\"	needed;  use .AS below instead)
.\"
.\" .AS ?type? ?name?
.\"	Give maximum sizes of arguments for setting tab stops.  Type and
.\"	name are examples of largest possible arguments that will be passed
.\"	to .AP later.  If args are omitted, default tab stops are used.
.\"
.\" .BS
.\"	Start box enclosure.  From here until next .BE, everything will be
.\"	enclosed in one large box.
.\"
.\" .BE
.\"	End of box enclosure.
.\"
.\" .CS
.\"	Begin code excerpt.
.\"
.\" .CE
.\"	End code excerpt.
.\"
.\" .VS ?version? ?br?
.\"	Begin vertical sidebar, for use in marking newly-changed parts
.\"	of man pages.  The first argument is ignored and used for recording
.\"	the version when the .VS was added, so that the sidebars can be
.\"	found and removed when they reach a certain age.  If another argument
.\"	is present, then a line break is forced before starting the sidebar.
.\"
.\" .VE
.\"	End of vertical sidebar.
.\"
.\" .DS
.\"	Begin an indented unfilled display.
.\"
.\" .DE
.\"	End of indented unfilled display.
.\"
.\" .SO ?manpage?
.\"	Start of list of standard options for a Tk widget. The manpage
.\"	argument defines where to look up the standard options; if
.\"	omitted, defaults to "options". The options follow on successive
.\"	lines, in three columns separated by tabs.
.\"
.\" .SE
.\"	End of list of standard options for a Tk widget.
.\"
.\" .OP cmdName dbName dbClass
.\"	Start of description of a specific option.  cmdName gives the
.\"	option's name as specified in the class command, dbName gives
.\"	the option's name in the option database, and dbClass gives
.\"	the option's class in the option database.
.\"
.\" .UL arg1 arg2
.\"	Print arg1 underlined, then print arg2 normally.
.\"
.\" .QW arg1 ?arg2?
.\"	Print arg1 in quotes, then arg2 normally (for trailing punctuation).
.\"
.\" .PQ arg1 ?arg2?
.\"	Print an open parenthesis, arg1 in quotes, then arg2 normally
.\"	(for trailing punctuation) and then a closing parenthesis.
.\"
.\"	# Set up traps and other miscellaneous stuff for Tcl/Tk man pages.
.if t .wh -1.3i ^B
.nr ^l \n(.l
.ad b
.\"	# Start an argument description
.de AP
.ie !"\\$4"" .TP \\$4
.el \{\
.   ie !"\\$2"" .TP \\n()Cu
.   el          .TP 15
.\}
.ta \\n()Au \\n()Bu
.ie !"\\$3"" \{\
\&\\$1 \\fI\\$2\\fP (\\$3)
.\".b
.\}
.el \{\
.br
.ie !"\\$2"" \{\
\&\\$1	\\fI\\$2\\fP
.\}
.el \{\
\&\\fI\\$1\\fP
.\}
.\}
..
.\"	# define tabbing values for .AP
.de AS
.nr )A 10n
.if !"\\$1"" .nr )A \\w'\\$1'u+3n
.nr )B \\n()Au+15n
.\"
.if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n
.nr )C \\n()Bu+\\w'(in/out)'u+2n
..
.AS Tcl_Interp Tcl_CreateInterp in/out
.\"	# BS - start boxed text
.\"	# ^y = starting y location
.\"	# ^b = 1
.de BS
.br
.mk ^y
.nr ^b 1u
.if n .nf
.if n .ti 0
.if n \l'\\n(.lu\(ul'
.if n .fi
..
.\"	# BE - end boxed text (draw box now)
.de BE
.nf
.ti 0
.mk ^t
.ie n \l'\\n(^lu\(ul'
.el \{\
.\"	Draw four-sided box normally, but don't draw top of
.\"	box if the box started on an earlier page.
.ie !\\n(^b-1 \{\
\h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul'
.\}
.el \}\
\h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul'
.\}
.\}
.fi
.br
.nr ^b 0
..
.\"	# VS - start vertical sidebar
.\"	# ^Y = starting y location
.\"	# ^v = 1 (for troff;  for nroff this doesn't matter)
.de VS
.if !"\\$2"" .br
.mk ^Y
.ie n 'mc \s12\(br\s0
.el .nr ^v 1u
..
.\"	# VE - end of vertical sidebar
.de VE
.ie n 'mc
.el \{\
.ev 2
.nf
.ti 0
.mk ^t
\h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n'
.sp -1
.fi
.ev
.\}
.nr ^v 0
..
.\"	# Special macro to handle page bottom:  finish off current
.\"	# box/sidebar if in box/sidebar mode, then invoked standard
.\"	# page bottom macro.
.de ^B
.ev 2
'ti 0
'nf
.mk ^t
.if \\n(^b \{\
.\"	Draw three-sided box if this is the box's first page,
.\"	draw two sides but no top otherwise.
.ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c
.el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c
.\}
.if \\n(^v \{\
.nr ^x \\n(^tu+1v-\\n(^Yu
\kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c
.\}
.bp
'fi
.ev
.if \\n(^b \{\
.mk ^y
.nr ^b 2
.\}
.if \\n(^v \{\
.mk ^Y
.\}
..
.\"	# DS - begin display
.de DS
.RS
.nf
.sp
..
.\"	# DE - end display
.de DE
.fi
.RE
.sp
..
.\"	# SO - start of list of standard options
.de SO
'ie '\\$1'' .ds So \\fBoptions\\fR
'el .ds So \\fB\\$1\\fR
.SH "STANDARD OPTIONS"
.LP
.nf
.ta 5.5c 11c
.ft B
..
.\"	# SE - end of list of standard options
.de SE
.fi
.ft R
.LP
See the \\*(So manual entry for details on the standard options.
..
.\"	# OP - start of full description for a single option
.de OP
.LP
.nf
.ta 4c
Command-Line Name:	\\fB\\$1\\fR
Database Name:	\\fB\\$2\\fR
Database Class:	\\fB\\$3\\fR
.fi
.IP
..
.\"	# CS - begin code excerpt
.de CS
.RS
.nf
.ta .25i .5i .75i 1i
..
.\"	# CE - end code excerpt
.de CE
.fi
.RE
..
.\"	# UL - underline word
.de UL
\\$1\l'|0\(ul'\\$2
..
.\"	# QW - apply quotation marks to word
.de QW
.ie '\\*(lq'"' ``\\$1''\\$2
.\"" fix emacs highlighting
.el \\*(lq\\$1\\*(rq\\$2
..
.\"	# PQ - apply parens and quotation marks to word
.de PQ
.ie '\\*(lq'"' (``\\$1''\\$2)\\$3
.\"" fix emacs highlighting
.el (\\*(lq\\$1\\*(rq\\$2)\\$3
..
.\"	# QR - quoted range
.de QR
.ie '\\*(lq'"' ``\\$1''\\-``\\$2''\\$3
.\"" fix emacs highlighting
.el \\*(lq\\$1\\*(rq\\-\\*(lq\\$2\\*(rq\\$3
..
.\"	# MT - "empty" string
.de MT
.QW ""
..
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
lindex \- Retrieve an element from a list
.SH SYNOPSIS
\fBlindex \fIlist\fR ?\fIindex ...\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
\fBlindex \fIlist\fR
.CE
.PP
or
.PP
.CS
\fBlindex \fIlist\fR {}
.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
\fBlindex\fR $a 1 2 3
.CE
.PP
or
.PP
.CS
\fBlindex\fR $a {1 2 3}
.CE
.PP
is synonymous with
.PP
.CS
\fBlindex\fR [\fBlindex\fR [\fBlindex\fR $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), lassign(n), ledit(n), linsert(n), llength(n),
lmap(n), lpop(n), lrange(n), lremove(n), lrepeat(n), lreplace(n),
lreverse(n), lsearch(n), lseq(n), lset(n), lsort(n),
string(n)
.SH KEYWORDS
element, index, list
'\"Local Variables:
'\"mode: nroff
'\"End:
