variable - create and initialize a namespace variable


variable ?name value...? name ?value?


This command is normally used within a namespace eval command to create one or more variables within a namespace. Each variable name is initialized with value. The value for the last variable is optional.

If a variable name does not exist, it is created. In this case, if value is specified, it is assigned to the newly created variable. If no value is specified, the new variable is left undefined. If the variable already exists, it is set to value if value is specified or left unchanged if no value is given. Normally, name is unqualified (does not include the names of any containing namespaces), and the variable is created in the current namespace. If name includes any namespace qualifiers, the variable is created in the specified namespace. If the variable is not defined, it will be visible to the namespace which command, but not to the info exists command.

If the variable command is executed inside a Tcl procedure, it creates local variables linked to the corresponding namespace variables (and therefore these variables are listed by info vars.) In this way the variable command resembles the global command, although the global command only links to variables in the global namespace. If any values 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.

A name argument cannot reference an element within an array. Instead, name should reference the entire array, and the initialization value should be left off. After the variable has been declared, elements within the array can be set using ordinary set or array commands.


Create a variable in a namespace:
namespace eval foo {
    variable bar 12345

Create an array in a namespace:

namespace eval someNS {
    variable someAry
    array set someAry {
        someName  someValue
        otherName otherValue

Access variables in namespaces from a procedure:

namespace eval foo {
    proc spong {} {
        # Variable in this namespace
        variable bar
        puts "bar is $bar"

        # Variable in another namespace
        variable ::someNS::someAry
        parray someAry


global, namespace, upvar


global, namespace, procedure, variable
Copyright © 1993-1997 Bell Labs Innovations for Lucent Technologies
Copyright © 1997 Sun Microsystems, Inc.
Copyright © 1995-1997 Roger E. Critchlow Jr.