if.n

来自「linux系统下的音频通信」· N 代码 · 共 44 行

'\"
'\" Copyright (c) 1993 The Regents of the University of California.
'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
'\" SCCS: @(#) if.n 1.7 96/08/26 13:00:00
'\" 
.so man.macros
.TH if n "" Tcl "Tcl Built-In Commands"
.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 ... ?\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
(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);
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