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man pages section 1: User Commands

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Updated: Wednesday, February 9, 2022

variable (1t)


variable - create and initialize a namespace variable


variable name

variable ?name value...?


variable(1t)                 Tcl Built-In Commands                variable(1t)


       variable - create and initialize a namespace variable

       variable name

       variable ?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  ini-
       tialized 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  names-
       pace.  If the variable is not defined, it will be visible to the names-
       pace 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 com-
       mand resolves variable names  with  respect  to  the  global  namespace
       instead  of  the current namespace of the procedure.  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

       See attributes(7) for descriptions of the following attributes:

       |Availability   | runtime/tcl-8    |
       |Stability      | Uncommitted      |

       global(n), namespace(n), upvar(n)

       global, namespace, procedure, variable

       Source  code  for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source was downloaded from  http://prdownloads.sourceforge.net/tcl/tcl-

       Further information about this software can be found on the open source
       community website at https://www.tcl.tk/.

Tcl                                   8.0                         variable(1t)