source: downloads/tcl8.5.2/doc/variable.n @ 44

'\"
'\" Copyright (c) 1993-1997 Bell Labs Innovations for Lucent Technologies
'\" Copyright (c) 1997 Sun Microsystems, Inc.
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\" 
'\" RCS: @(#) $Id: variable.n,v 1.8 2005/05/10 18:34:04 kennykb Exp $
'\" 
.so man.macros
.TH variable n 8.0 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
variable \- create and initialize a namespace variable
.SH SYNOPSIS
\fBvariable \fR?\fIname value...\fR? \fIname \fR?\fIvalue\fR?
.BE

.SH DESCRIPTION
.PP
This command is normally used within a
\fBnamespace eval\fR command to create one or more variables
within a namespace.
Each variable \fIname\fR is initialized with \fIvalue\fR.
The \fIvalue\fR for the last variable is optional.
.PP
If a variable \fIname\fR does not exist, it is created.
In this case, if \fIvalue\fR is specified,
it is assigned to the newly created variable.
If no \fIvalue\fR is specified, the new variable is left undefined.
If the variable already exists,
it is set to \fIvalue\fR if \fIvalue\fR is specified
or left unchanged if no \fIvalue\fR is given.
Normally, \fIname\fR is unqualified
(does not include the names of any containing namespaces),
and the variable is created in the current namespace.
If \fIname\fR includes any namespace qualifiers,
the variable is created in the specified namespace.  If the variable
is not defined, it will be visible to the \fBnamespace which\fR
command, but not to the \fBinfo exists\fR command.
.PP
If the \fBvariable\fR command is executed inside a Tcl procedure,
it creates local variables
linked to the corresponding namespace variables (and therefore these
variables are listed by \fBinfo vars\fR.)
In this way the \fBvariable\fR command resembles the \fBglobal\fR command,
although the \fBglobal\fR command
only links to variables in the global namespace.
If any \fIvalue\fRs are given,
they are used to modify the values of the associated namespace variables.
If a namespace variable does not exist,
it is created and optionally initialized.
.PP
A \fIname\fR argument cannot reference an element within an array.
Instead, \fIname\fR should reference the entire array,
and the initialization \fIvalue\fR should be left off.
After the variable has been declared,
elements within the array can be set using ordinary
\fBset\fR or \fBarray\fR commands.
.SH EXAMPLES
Create a variable in a namespace:
.CS
namespace eval foo {
    \fBvariable\fR bar 12345
}
.CE
.PP
Create an array in a namespace:
.CS
namespace eval someNS {
    \fBvariable\fR someAry
    array set someAry {
        someName  someValue
        otherName otherValue
    }
}
.CE
.PP
Access variables in namespaces from a procedure:
.CS
namespace eval foo {
    proc spong {} {
        # Variable in this namespace
        \fBvariable\fR bar
        puts "bar is $bar"

        # Variable in another namespace
        \fBvariable\fR ::someNS::someAry
        parray someAry
    }
}
.CE

.SH "SEE ALSO"
global(n), namespace(n), upvar(n)

.SH KEYWORDS
global, namespace, procedure, variable