namespace(n)                 Tcl Built-In Commands                namespace(n)


       namespace - create and manipulate contexts for commands and variables

       namespace ?option? ?arg ...?

       The  namespace  command  lets  you create, access, and destroy separate
       contexts for commands and variables.  See the section WHAT IS A  NAMES-
       PACE? below for a brief overview of namespaces.  The legal option's are
       listed below.  Note that you can abbreviate the option's.

       namespace children ?namespace? ?pattern?
              Returns a list of all child namespaces that belong to the names-
              pace  namespace.   If namespace is not specified, then the chil-
              dren are returned  for  the  current  namespace.   This  command
              returns  fully-qualified  names,  which  start  with ::.  If the
              optional pattern is given, then this command  returns  only  the
              names  that  match  the  glob-style pattern.  The actual pattern
              used is determined as follows: a pattern that starts with ::  is
              used  directly, otherwise the namespace namespace (or the fully-
              qualified name of the current namespace) is prepended  onto  the
              the pattern.

       namespace code script
              Captures  the  current  namespace context for later execution of
              the script script.  It returns a new script in which script  has
              been  wrapped  in  a namespace code command.  The new script has
              two important properties.  First, it can  be  evaluated  in  any
              namespace  and  will cause script to be evaluated in the current
              namespace  (the  one  where  the  namespace  code  command   was
              invoked).   Second,  additional arguments can be appended to the
              resulting script and they will be passed to script as additional
              arguments.   For example, suppose the command set script [names-
              pace code {foo bar}] is invoked in namespace ::a::b.  Then  eval
              "$script  x  y"  can  be executed in any namespace (assuming the
              value of script has been passed in properly) and will  have  the
              same  effect as the command namespace eval ::a::b {foo bar x y}.
              This command is needed because extensions like Tk normally  exe-
              cute callback scripts in the global namespace.  A scoped command
              captures a command together with its namespace context in a  way
              that  allows  it to be executed properly later.  See the section
              SCOPED VALUES for some examples of how this is  used  to  create
              callback scripts.

       namespace current
              Returns the fully-qualified name for the current namespace.  The
              actual name of the global namespace  is  ``''  (i.e.,  an  empty
              string), but this command returns :: for the global namespace as
              a convenience to programmers.

       namespace delete ?namespace namespace ...?
              Each namespace namespace is deleted and  all  variables,  proce-
              dures,  and  child  namespaces  contained  in  the namespace are
              deleted.  If a  procedure  is  currently  executing  inside  the
              namespace,  the namespace will be kept alive until the procedure
              returns; however, the namespace is marked to prevent other  code
              from  looking it up by name.  If a namespace doesn't exist, this
              command returns an error.  If no namespace names are given, this
              command does nothing.

       namespace eval namespace arg ?arg ...?
              Activates  a  namespace called namespace and evaluates some code
              in that context.  If the namespace does not already exist, it is
              created.   If more than one arg argument is specified, the argu-
              ments are concatenated together with a space between each one in
              the  same  fashion as the eval command, and the result is evalu-

              If namespace has leading namespace qualifiers  and  any  leading
              namespaces do not exist, they are automatically created.

       namespace export ?-clear? ?pattern pattern ...?
              Specifies  which  commands  are  exported from a namespace.  The
              exported commands are those that  can  be  later  imported  into
              another  namespace  using a namespace import command.  Both com-
              mands defined in a namespace and commands the namespace has pre-
              viously  imported  can be exported by a namespace.  The commands
              do not have to be defined at the time the namespace export  com-
              mand  is  executed.  Each pattern may contain glob-style special
              characters, but it may not  include  any  namespace  qualifiers.
              That  is,  the  pattern can only specify commands in the current
              (exporting) namespace.  Each pattern is appended onto the names-
              pace's  list  of  export patterns.  If the -clear flag is given,
              the namespace's export pattern list is reset to empty before any
              pattern  arguments  are  appended.  If no patterns are given and
              the -clear flag isn't given, this  command  returns  the  names-
              pace's current export list.

       namespace forget ?pattern pattern ...?
              Removes  previously  imported  commands  from a namespace.  Each
              pattern is a qualified name such as foo::x or a::b::p*.   Quali-
              fied  names  contain ::s and qualify a name with the name of one
              or more namespaces.  Each pattern is qualified with the name  of
              an  exporting  namespace and may have glob-style special charac-
              ters in the command name at the end of the qualified name.  Glob
              characters  may  not  appear  in a namespace name.  This command
              first finds the matching  exported  commands.   It  then  checks
              whether  any of those those commands were previously imported by
              the current namespace.  If so, this command deletes  the  corre-
              sponding  imported commands.  In effect, this un-does the action
              of a namespace import command.

       namespace import ?-force? ?pattern pattern ...?
              Imports commands into a namespace.  Each pattern is a  qualified
              name  like foo::x or a::p*.  That is, it includes the name of an
              exporting namespace and may have glob-style  special  characters
              in  the  command  name  at  the end of the qualified name.  Glob
              characters may not appear in a namespace name.  All the commands
              that  match  a  pattern  string and which are currently exported
              from their namespace are added to the current  namespace.   This
              is  done by creating a new command in the current namespace that
              points to the exported command in its original  namespace;  when
              the new imported command is called, it invokes the exported com-
              mand.  This command normally returns an  error  if  an  imported
              command  conflicts  with  an  existing command.  However, if the
              -force option is given, imported commands will silently  replace
              existing  commands.   The  namespace import command has snapshot
              semantics: that is, only requested commands that  are  currently
              defined  in  the  exporting  namespace  are  imported.  In other
              words, you can import only the commands that are in a  namespace
              at  the  time when the namespace import command is executed.  If
              another command is defined and exported in this namespace  later
              on, it will not be imported.

       namespace inscope namespace arg ?arg ...?
              Executes  a  script  in  the  context of a particular namespace.
              This command is not expected to be used directly by programmers;
              calls  to  it  are  generated  implicitly  when applications use
              namespace code commands to  create  callback  scripts  that  the
              applications  then  register with, e.g., Tk widgets.  The names-
              pace inscope command is much like  the  namespace  eval  command
              except  that  it  has  lappend  semantics and the namespace must
              already exist.  It treats the first  argument  as  a  list,  and
              appends  any  arguments  after  the first onto the end as proper
              list elements.  namespace inscope ::foo a x y z is equivalent to
              namespace eval ::foo [concat a [list x y z]] This lappend seman-
              tics is important because many  callback  scripts  are  actually

       namespace origin command
              Returns  the  fully-qualified  name  of  the original command to
              which the imported command command refers.  When  a  command  is
              imported  into  a  namespace,  a  new command is created in that
              namespace that points to the actual  command  in  the  exporting
              namespace.   If  a command is imported into a sequence of names-
              paces a, b,...,n where each successive  namespace  just  imports
              the  command  from  the previous namespace, this command returns
              the fully-qualified name of the original command  in  the  first
              namespace, a.  If command does not refer to an imported command,
              the command's own fully-qualified name is returned.

       namespace parent ?namespace?
              Returns the fully-qualified name of  the  parent  namespace  for
              namespace  namespace.  If namespace is not specified, the fully-
              qualified name of the current namespace's parent is returned.

       namespace qualifiers string
              Returns any leading namespace qualifiers for string.  Qualifiers
              are   namespace   names   separated  by  ::s.   For  the  string
              ::foo::bar::x, this command returns ::foo::bar, and  for  ::  it
              returns  an empty string.  This command is the complement of the
              namespace tail command.  Note that it does not check whether the
              namespace  names  are,  in  fact, the names of currently defined

       namespace tail string
              Returns the simple name at the end of a qualified string.  Qual-
              ifiers  are  namespace  names  separated by ::s.  For the string
              ::foo::bar::x, this command returns x, and for :: it returns  an
              empty  string.   This command is the complement of the namespace
              qualifiers command.  It does not  check  whether  the  namespace
              names are, in fact, the names of currently defined namespaces.

       namespace which ?-command? ?-variable? name
              Looks  up  name  as either a command or variable and returns its
              fully-qualified name.  For example, if name does  not  exist  in
              the  current  namespace  but does exist in the global namespace,
              this command returns a fully-qualified name in the global names-
              pace.   If  the command or variable does not exist, this command
              returns an empty string.  If the variable has been  created  but
              not  defined,  such  as  with  the variable command or through a
              trace on the variable, this command will return the fully-quali-
              fied name of the variable.  If no flag is given, name is treated
              as a command name.  See the section NAME RESOLUTION below for an
              explanation of the rules regarding name resolution.

       A namespace is a collection of commands and variables.  It encapsulates
       the commands and variables to ensure that they won't interfere with the
       commands  and  variables  of  other namespaces.  Tcl has always had one
       such collection, which we refer to as the global namespace.  The global
       namespace  holds all global variables and commands.  The namespace eval
       command lets you create new namespaces.  For example,
              namespace eval Counter {
                  namespace export bump
                  variable num 0

                  proc bump {} {
                      variable num
                      incr num
       creates a new namespace containing the variable num and  the  procedure
       bump.   The  commands and variables in this namespace are separate from
       other commands and variables in the same program.  If there is  a  com-
       mand  named  bump in the global namespace, for example, it will be dif-
       ferent from the command bump in the Counter namespace.

       Namespace variables resemble global variables in Tcl.  They exist  out-
       side  of  the procedures in a namespace but can be accessed in a proce-
       dure via the variable command, as shown in the example above.

       Namespaces are dynamic.  You can add and delete commands and  variables
       at  any time, so you can build up the contents of a namespace over time
       using a series of namespace eval commands.  For example, the  following
       series  of  commands  has  the  same effect as the namespace definition
       shown above:
              namespace eval Counter {
                  variable num 0
                  proc bump {} {
                      variable num
                      return [incr num]
              namespace eval Counter {
                  proc test {args} {
                      return $args
              namespace eval Counter {
                  rename test ""
       Note that the test procedure is added to  the  Counter  namespace,  and
       later removed via the rename command.

       Namespaces  can have other namespaces within them, so they nest hierar-
       chically.  A nested namespace is encapsulated inside its parent  names-
       pace and can not interfere with other namespaces.

       Each  namespace  has  a textual name such as history or ::safe::interp.
       Since namespaces may nest, qualified names are used to  refer  to  com-
       mands,  variables,  and  child  namespaces contained inside namespaces.
       Qualified names are similar to the hierarchical  path  names  for  Unix
       files or Tk widgets, except that :: is used as the separator instead of
       / or ..  The topmost or global namespace has the name  ``''  (i.e.,  an
       empty  string),  although  ::  is  a  synonym.  As an example, the name
       ::safe::interp::create refers to the command create  in  the  namespace
       interp that is a child of of namespace ::safe, which in turn is a child
       of the global namespace ::.

       If you want to access commands and variables  from  another  namespace,
       you  must use some extra syntax.  Names must be qualified by the names-
       pace that contains them.  From the global namespace,  we  might  access
       the Counter procedures like this:
              Counter::bump 5
       We could access the current count like this:
              puts "count = $Counter::num"
       When  one namespace contains another, you may need more than one quali-
       fier to reach its elements.  If we had a namespace Foo  that  contained
       the  namespace  Counter,  you  could invoke its bump procedure from the
       global namespace like this:
              Foo::Counter::bump 3

       You can also use qualified names when you create and  rename  commands.
       For example, you could add a procedure to the Foo namespace like this:
              proc Foo::Test {args} {return $args}
       And you could move the same procedure to another namespace like this:
              rename Foo::Test Bar::Test

       There  are  a few remaining points about qualified names that we should
       cover.  Namespaces have nonempty names except for the global namespace.
       ::  is  disallowed  in  simple  command,  variable, and namespace names
       except as a namespace separator.  Extra :s  in  a  qualified  name  are
       ignored;  that is, two or more :s are treated as a namespace separator.
       A trailing :: in a qualified variable or command  name  refers  to  the
       variable  or  command  named {}.  However, a trailing :: in a qualified
       namespace name is ignored.

       In general, all Tcl commands that take variable and command names  sup-
       port  qualified names.  This means you can give qualified names to such
       commands as set, proc, rename, and interp  alias.   If  you  provide  a
       fully-qualified  name that starts with a ::, there is no question about
       what command, variable, or namespace you mean.  However,  if  the  name
       does  not start with a :: (i.e., is relative), Tcl follows a fixed rule
       for looking it up: Command and variable names are  always  resolved  by
       looking  first  in the current namespace, and then in the global names-
       pace.  Namespace names, on the other hand, are always resolved by look-
       ing in only the current namespace.

       In the following example,
              set traceLevel 0
              namespace eval Debug {
                  printTrace $traceLevel
       Tcl  looks for traceLevel in the namespace Debug and then in the global
       namespace.  It looks up the command printTrace in the same way.   If  a
       variable  or  command  name is not found in either context, the name is
       undefined.  To make this point absolutely clear, consider the following
              set traceLevel 0
              namespace eval Foo {
                  variable traceLevel 3

                  namespace eval Debug {
                      printTrace $traceLevel
       Here Tcl looks for traceLevel first in the namespace Foo::Debug.  Since
       it is not found there, Tcl then looks for it in the  global  namespace.
       The variable Foo::traceLevel is completely ignored during the name res-
       olution process.

       You can use the namespace which command to clear up any question  about
       name resolution.  For example, the command:
              namespace eval Foo::Debug {namespace which -variable traceLevel}
       returns ::traceLevel.  On the other hand, the command,
              namespace eval Foo {namespace which -variable traceLevel}
       returns ::Foo::traceLevel.

       As  mentioned above, namespace names are looked up differently than the
       names of variables and commands.  Namespace names are  always  resolved
       in  the  current  namespace.  This means, for example, that a namespace
       eval command that creates a new namespace always creates a child of the
       current namespace unless the new namespace name begins with a ::.

       Tcl  has no access control to limit what variables, commands, or names-
       paces you can reference.  If you provide a qualified name that resolves
       to  an  element  by  the name resolution rule above, you can access the

       You can access a namespace variable from a procedure in the same names-
       pace by using the variable command.  Much like the global command, this
       creates a local link to the namespace variable.  If necessary, it  also
       creates the variable in the current namespace and initializes it.  Note
       that the global command only creates links to variables in  the  global
       namespace.  It is not necessary to use a variable command if you always
       refer to the namespace variable using an appropriate qualified name.

       Namespaces are often used to represent libraries.   Some  library  com-
       mands are used so frequently that it is a nuisance to type their quali-
       fied names.  For example, suppose that all of the commands in a package
       like  BLT  are  contained  in  a  namespace called Blt.  Then you might
       access these commands like this:
              Blt::graph .g -background red
              Blt::table . .g 0,0
       If you use the graph and table commands frequently,  you  may  want  to
       access them without the Blt:: prefix.  You can do this by importing the
       commands into the current namespace, like this:
              namespace import Blt::*
       This adds all exported commands from the Blt namespace into the current
       namespace context, so you can write code like this:
              graph .g -background red
              table . .g 0,0
       The  namespace  import  command  only imports commands from a namespace
       that that namespace exported with a namespace export command.

       Importing every command from a namespace is generally a bad idea  since
       you don't know what you will get.  It is better to import just the spe-
       cific commands you need.  For example, the command
              namespace import Blt::graph Blt::table
       imports only the graph and table commands into the current context.

       If you try to import a command that already exists,  you  will  get  an
       error.  This prevents you from importing the same command from two dif-
       ferent packages.  But from time to time (perhaps when  debugging),  you
       may  want  to get around this restriction.  You may want to reissue the
       namespace import command to pick up new commands that have appeared  in
       a namespace.  In that case, you can use the -force option, and existing
       commands will be silently overwritten:
              namespace import -force Blt::graph Blt::table
       If for some reason, you want to stop using the imported  commands,  you
       can remove them with an namespace forget command, like this:
              namespace forget Blt::*
       This searches the current namespace for any commands imported from Blt.
       If it finds any, it removes them.  Otherwise, it does  nothing.   After
       this, the Blt commands must be accessed with the Blt:: prefix.

       When you delete a command from the exporting namespace like this:
              rename Blt::graph ""
       the  command  is  automatically removed from all namespaces that import

       You can export commands from a namespace like this:
              namespace eval Counter {
                  namespace export bump reset
                  variable Num 0
                  variable Max 100

                  proc bump {{by 1}} {
                      variable Num
                      incr Num $by
                      return $Num
                  proc reset {} {
                      variable Num
                      set Num 0
                  proc Check {} {
                      variable Num
                      variable Max
                      if {$Num > $Max} {
                          error "too high!"
       The procedures bump and reset are exported, so they are  included  when
       you import from the Counter namespace, like this:
              namespace import Counter::*
       However,  the  Check procedure is not exported, so it is ignored by the
       import operation.

       The namespace import command only imports commands that  were  declared
       as exported by their namespace.  The namespace export command specifies
       what commands may be imported by  other  namespaces.   If  a  namespace
       import command specifies a command that is not exported, the command is
       not imported.


       exported, internal, variable

Tcl                                   8.0                         namespace(n)