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1994-05-08
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240 lines
'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" All rights reserved.
'\"
'\" Permission is hereby granted, without written agreement and without
'\" license or royalty fees, to use, copy, modify, and distribute this
'\" documentation for any purpose, provided that the above copyright
'\" notice and the following two paragraphs appear in all copies.
'\"
'\" IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
'\" FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
'\" ARISING OUT OF THE USE OF THIS DOCUMENTATION, EVEN IF THE UNIVERSITY OF
'\" CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
'\"
'\" THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
'\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
'\" AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
'\" ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATION TO
'\" PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
'\"
'\" $Header: /user6/ouster/tcl/man/RCS/if.n,v 1.1 93/05/03 17:34:01 ouster Exp $ SPRITE (Berkeley)
'\"
.\" The definitions below are for supplemental macros used in Tcl/Tk
.\" manual entries.
.\"
.\" .HS name section [date [version]]
.\" Replacement for .TH in other man pages. See below for valid
.\" section names.
.\"
.\" .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
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.\"
.\" .VS
.\" Begin vertical sidebar, for use in marking newly-changed parts
.\" of man pages.
.\"
.\" .VE
.\" End of vertical sidebar.
.\"
.\" .DS
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.\"
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.\"
'\" # Heading for Tcl/Tk man pages
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.\"
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..
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'\" # ^Y = starting y location
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.sp -1
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.ev
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.nr ^v 0
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'\" # Special macro to handle page bottom: finish off current
'\" # box/sidebar if in box/sidebar mode, then invoked standard
'\" # page bottom macro.
.de ^B
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.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
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.nr ^x \\n(^tu+1v-\\n(^Yu
\kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c
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..
'\" # DS - begin display
.de DS
.RS
.nf
.sp
..
'\" # DE - end display
.de DE
.fi
.RE
.sp .5
..
.HS if tcl
.BS
'\" Note: do not modify the .SH NAME line immediately below!
.SH NAME
if \- Execute scripts conditionally
.SH SYNOPSIS
\fBif \fIexpr1 \fR?\fBthen\fR? \fIbody1 \fBelseif \fIexpr2 \fR?\fBthen\fR? \fIbody2\fR \fBelseif\fR ... \fR?\fBelse\fR? ?\fIbodyN\fR?
.BE
.SH DESCRIPTION
.PP
The \fIif\fR command evaluates \fIexpr1\fR as an expression (in the
same way that \fBexpr\fR evaluates its argument). The value of the
expression must be a boolean
.VS
(a numeric value, where 0 is false and
anything is true, or a string value such as \fBtrue\fR or \fByes\fR
for true and \fBfalse\fR or \fBno\fR for false);
.VE
if it is true then \fIbody1\fR is executed by passing it to the
Tcl interpreter.
Otherwise \fIexpr2\fR is evaluated as an expression and if it is true
then \fBbody2\fR is executed, and so on.
If none of the expressions evaluates to true then \fIbodyN\fR is
executed.
The \fBthen\fR and \fBelse\fR arguments are optional
``noise words'' to make the command easier to read.
There may be any number of \fBelseif\fR clauses, including zero.
\fIBodyN\fR may also be omitted as long as \fBelse\fR is omitted too.
The return value from the command is the result of the body script
that was executed, or an empty string
if none of the expressions was non-zero and there was no \fIbodyN\fR.
.SH KEYWORDS
boolean, conditional, else, false, if, true