NAME
       interp - Create and manipulate Tcl interpreters

SYNOPSIS
       interp option ?arg arg ...?


DESCRIPTION
       This  command  makes  it  possible to create one or more new Tcl inter-
       preters that co-exist with the creating interpreter in the same  appli-
       cation.   The  creating  interpreter  is  called the master and the new
       interpreter is called a slave.  A  master  can  create  any  number  of
       slaves, and each slave can itself create additional slaves for which it
       is master, resulting in a hierarchy of interpreters.

       Each interpreter is independent from the others: it has  its  own  name
       space  for commands, procedures, and global variables.  A master inter-
       preter may create connections between its slaves  and  itself  using  a
       mechanism  called  an  alias.   An alias is a command in a slave inter-
       preter which, when invoked, causes a command to be invoked in its  mas-
       ter  interpreter  or in another slave interpreter.  The only other con-
       nections between interpreters are through  environment  variables  (the
       env  variable), which are normally shared among all interpreters in the
       application. Note that the name space for  files  (such  as  the  names
       returned by the open command) is no longer shared between interpreters.
       Explicit commands are provided to share files and  to  transfer  refer-
       ences to open files from one interpreter to another.

       The interp command also provides support for safe interpreters.  A safe
       interpreter is a slave whose functions have been greatly restricted, so
       that  it is safe to execute untrusted scripts without fear of them dam-
       aging other interpreters or the application's environment. For example,
       all  IO  channel creation commands and subprocess creation commands are
       made inaccessible to safe interpreters.  See  SAFE  INTERPRETERS  below
       for  more  information  on  what  features are present in a safe inter-
       preter.  The dangerous functionality  is  not  removed  from  the  safe
       interpreter;  instead,  it is hidden, so that only trusted interpreters
       can obtain access to it. For a detailed explanation of hidden commands,
       see  HIDDEN  COMMANDS, below.  The alias mechanism can be used for pro-
       tected communication (analogous to  a  kernel  call)  between  a  slave
       interpreter  and  its  master.   See  ALIAS INVOCATION, below, for more
       details on how the alias mechanism works.

       A qualified interpreter name is a proper Tcl lists containing a  subset
       of its ancestors in the interpreter hierarchy, terminated by the string
       naming the interpreter in its immediate master. Interpreter  names  are
       relative  to  the interpreter in which they are used. For example, if a
       is a slave of the current interpreter and it has a slave a1,  which  in
       turn  has  a  slave  a11, the qualified name of a11 in a is the list a1
       a11.

       The interp command,  described  below,  accepts  qualified  interpreter
       names as arguments; the interpreter in which the command is being eval-
       uated can always be referred to as {} (the empty list or string).  Note
       that  it  is  impossible to refer to a master (ancestor) interpreter by
       name in a slave interpreter except through aliases. Also, there  is  no
       global  name by which one can refer to the first interpreter created in
       an application.  Both restrictions are motivated by safety concerns.

THE INTERP COMMAND
       The interp command is used to  create,  delete,  and  manipulate  slave
       interpreters,  and  to share or transfer channels between interpreters.
       It can have any of several forms, depending on the option argument:

       interp alias srcPath srcToken
              Returns a Tcl list whose elements are  the  targetCmd  and  args
              associated  with  the alias represented by srcToken (this is the
              value returned when the alias was created; it is  possible  that
              the  name  of  the source command in the slave is different from
              srcToken).

       interp alias srcPath srcToken {}
              Deletes the alias for srcToken in the slave interpreter  identi-
              fied by srcPath.  srcToken refers to the value returned when the
              alias was created;  if the source command has been renamed,  the
              renamed command will be deleted.

       interp alias srcPath srcCmd targetPath targetCmd ?arg arg ...?
              This command creates an alias between one slave and another (see
              the alias slave command below for  creating  aliases  between  a
              slave  and  its  master).   In this command, either of the slave
              interpreters may be anywhere in the  hierarchy  of  interpreters
              under  the interpreter invoking the command.  SrcPath and srcCmd
              identify the source of the alias.  SrcPath is a Tcl  list  whose
              elements  select a particular interpreter.  For example, ``a b''
              identifies an interpreter b, which is a slave of interpreter  a,
              which  is  a  slave  of the invoking interpreter.  An empty list
              specifies the interpreter invoking the  command.   srcCmd  gives
              the  name  of a new command, which will be created in the source
              interpreter.  TargetPath and targetCmd specify a  target  inter-
              preter and command, and the arg arguments, if any, specify addi-
              tional arguments to targetCmd which are prepended to  any  argu-
              ments  specified  in the invocation of srcCmd.  TargetCmd may be
              undefined at the time of this call, or it may already exist;  it
              is  not  created  by  this  command.  The alias arranges for the
              given target command to be invoked  in  the  target  interpreter
              whenever  the  given  source  command  is  invoked in the source
              interpreter.  See ALIAS INVOCATION below for more details.   The
              command  returns  a  token  that uniquely identifies the command
              created srcCmd, even if the command is renamed  afterwards.  The
              token may but does not have to be equal to srcCmd.

       interp aliases ?path?
              This  command returns a Tcl list of the tokens of all the source
              commands for aliases defined in the  interpreter  identified  by
              path.  The  tokens  correspond  to  the values returned when the
              aliases were created (which may not be the same as  the  current
              names of the commands).

       interp create ?-safe? ?--? ?path?
              Creates  a  slave  interpreter identified by path and a new com-
              mand, called a slave command. The name of the slave  command  is
              the  last  component  of path. The new slave interpreter and the
              slave command are created in the interpreter identified  by  the
              path  obtained  by  removing  the  last component from path. For
              example, if path is a b c then a new slave interpreter and slave
              command named c are created in the interpreter identified by the
              path a b.  The slave command may be used to manipulate  the  new
              interpreter  as described below. If path is omitted, Tcl creates
              a unique name of the form interpx, where x is  an  integer,  and
              uses  it for the interpreter and the slave command. If the -safe
              switch is specified (or if the  master  interpreter  is  a  safe
              interpreter),  the  new  slave  interpreter will be created as a
              safe interpreter with limited functionality; otherwise the slave
              will  include  the  full  set of Tcl built-in commands and vari-
              ables. The -- switch can be used to mark the  end  of  switches;
              it  may be needed if path is an unusual value such as -safe. The
              result of the command is the name of the  new  interpreter.  The
              name  of a slave interpreter must be unique among all the slaves
              for its master;  an error occurs if a slave interpreter  by  the
              given name already exists in this master.  The initial recursion
              limit of the slave interpreter is set to the  current  recursion
              limit of its parent interpreter.

       interp delete ?path ...?
              Deletes  zero  or  more  interpreters given by the optional path
              arguments, and for each interpreter, it also deletes its slaves.
              The  command also deletes the slave command for each interpreter
              deleted.  For each path argument, if no interpreter by that name
              exists, the command raises an error.

       interp eval path arg ?arg ...?
              This  command  concatenates all of the arg arguments in the same
              fashion as the concat  command,  then  evaluates  the  resulting
              string  as  a  Tcl script in the slave interpreter identified by
              path. The result of this evaluation (including error information
              such  as  the  errorInfo  and  errorCode  variables, if an error
              occurs) is returned to the invoking interpreter.  Note that  the
              script  will  be  executed in the current context stack frame of
              the path interpreter; this is so that the implementations (in  a
              master  interpreter)  of aliases in a slave interpreter can exe-
              cute scripts in the slave that find out  information  about  the
              slave's current state and stack frame.

       interp exists path
              Returns   1  if a slave interpreter by the specified path exists
              in this master, 0 otherwise. If path is  omitted,  the  invoking
              interpreter is used.

       interp expose path hiddenName ?exposedCmdName?
              Makes the hidden command hiddenName exposed, eventually bringing
              it back under a new exposedCmdName name (this name is  currently
              accepted  only  if  it is a valid global name space name without
              any ::), in the interpreter denoted by path.  If an exposed com-
              mand  with the targeted name already exists, this command fails.
              Hidden commands are explained in more detail in HIDDEN COMMANDS,
              below.

       interp hide path exposedCmdName ?hiddenCmdName?
              Makes  the exposed command exposedCmdName hidden, renaming it to
              the hidden command hiddenCmdName, or keeping the  same  name  if
              hiddenCmdName  is not given, in the interpreter denoted by path.
              If a hidden command with the targeted name already exists,  this
              command  fails.  Currently both exposedCmdName and hiddenCmdName
              can not contain namespace qualifiers, or  an  error  is  raised.
              Commands to be hidden by interp hide are looked up in the global
              namespace even if the current namespace is not the  global  one.
              This prevents slaves from fooling a master interpreter into hid-
              ing the wrong command, by making the current namespace  be  dif-
              ferent  from  the  global one.  Hidden commands are explained in
              more detail in HIDDEN COMMANDS, below.

       interp hidden path
              Returns a list of the names of all hidden commands in the inter-
              preter identified by path.

       interp invokehidden path ?-global? hiddenCmdName ?arg ...?
              Invokes the hidden command hiddenCmdName with the arguments sup-
              plied in the interpreter denoted by path.  No  substitutions  or
              evaluation are applied to the arguments.  If the -global flag is
              present, the hidden command is invoked at the  global  level  in
              the  target  interpreter; otherwise it is invoked at the current
              call frame and can access local variables in that and outer call
              frames.   Hidden commands are explained in more detail in HIDDEN
              COMMANDS, below.

       interp issafe ?path?
              Returns 1 if the interpreter identified by the specified path is
              safe, 0 otherwise.

       interp marktrusted path
              Marks  the  interpreter  identified by path as trusted. Does not
              expose the hidden commands. This command  can  only  be  invoked
              from  a  trusted  interpreter.  The command has no effect if the
              interpreter identified by path is already trusted.

       interp recursionlimit path ?newlimit?
              Returns the maximum allowable nesting depth for the  interpreter
              specified  by  path.   If newlimit is specified, the interpreter
              recursion limit will  be  set  so  that  nesting  of  more  than
              newlimit  calls  to  Tcl_Eval()  and  related procedures in that
              interpreter will return an error.  The newlimit  value  is  also
              returned.  The newlimit value must be a positive integer between
              1 and the maximum value of a non-long integer on the platform.

              The command sets the maximum size of the Tcl call stack only. It
              cannot  by  itself  prevent stack overflows on the C stack being
              used by the application. If your machine has a limit on the size
              of  the C stack, you may get stack overflows before reaching the
              limit set by the command. If this happens, see  if  there  is  a
              mechanism  in your system for increasing the maximum size of the
              C stack.

       interp share srcPath channelId destPath
              Causes the IO channel identified by channelId to  become  shared
              between  the  interpreter  identified  by srcPath and the inter-
              preter identified by destPath. Both interpreters have  the  same
              permissions  on the IO channel.  Both interpreters must close it
              to close the underlying IO channel; IO channels accessible in an
              interpreter  are  automatically  closed  when  an interpreter is
              destroyed.

       interp slaves ?path?
              Returns a Tcl list of the names of all  the  slave  interpreters
              associated  with  the interpreter identified by path. If path is
              omitted, the invoking interpreter is used.

       interp target path alias
              Returns a Tcl list describing  the  target  interpreter  for  an
              alias.  The  alias  is  specified  with  an interpreter path and
              source command name, just as in interp alias above. The name  of
              the target interpreter is returned as an interpreter path, rela-
              tive to the invoking interpreter.  If the target interpreter for
              the  alias  is  the  invoking  interpreter then an empty list is
              returned. If the target interpreter for the  alias  is  not  the
              invoking  interpreter or one of its descendants then an error is
              generated.  The target command does not have to  be  defined  at
              the time of this invocation.

       interp transfer srcPath channelId destPath
              Causes  the  IO channel identified by channelId to become avail-
              able in the interpreter identified by destPath  and  unavailable
              in the interpreter identified by srcPath.

SLAVE COMMAND
       For  each  slave interpreter created with the interp command, a new Tcl
       command is created in the master interpreter with the same name as  the
       new  interpreter. This command may be used to invoke various operations
       on the interpreter.  It has the following general form:
              slave command ?arg arg ...?
       Slave is the name of the interpreter, and command and the  args  deter-
       mine  the  exact behavior of the command.  The valid forms of this com-
       mand are:

       slave aliases
              Returns a Tcl list whose elements are  the  tokens  of  all  the
              aliases  in slave.  The tokens correspond to the values returned
              when the aliases were created (which may not be the same as  the
              current names of the commands).

       slave alias srcToken
              Returns  a  Tcl  list  whose elements are the targetCmd and args
              associated with the alias represented by srcToken (this  is  the
              value  returned  when the alias was created; it is possible that
              the actual source command in the slave is different from  srcTo-
              ken).

       slave alias srcToken {}
              Deletes the alias for srcToken in the slave interpreter.  srcTo-
              ken refers to the value returned when the alias was created;  if
              the source command has been renamed, the renamed command will be
              deleted.

       slave alias srcCmd targetCmd ?arg ..?
              Creates an alias such that whenever srcCmd is invoked in  slave,
              targetCmd  is  invoked in the master.  The arg arguments will be
              passed to targetCmd as additional  arguments,  prepended  before
              any  arguments  passed  in  the invocation of srcCmd.  See ALIAS
              INVOCATION below for details.  The command returns a token  that
              uniquely identifies the command created srcCmd, even if the com-
              mand is renamed afterwards. The token may but does not  have  to
              be equal to srcCmd.

       slave eval arg ?arg ..?
              This  command  concatenates all of the arg arguments in the same
              fashion as the concat  command,  then  evaluates  the  resulting
              string  as a Tcl script in slave.  The result of this evaluation
              (including error information such as the errorInfo and errorCode
              variables,  if  an  error  occurs)  is  returned to the invoking
              interpreter.  Note that the script will be executed in the  cur-
              rent context stack frame of slave; this is so that the implemen-
              tations (in a master interpreter) of aliases in a  slave  inter-
              preter  can  execute scripts in the slave that find out informa-
              tion about the slave's current state and stack frame.

       slave expose hiddenName ?exposedCmdName?
              This command exposes the hidden command  hiddenName,  eventually
              bringing  it  back under a new exposedCmdName name (this name is
              currently accepted only if it is a valid global name space  name
              without  any ::), in slave.  If an exposed command with the tar-
              geted name already exists, this command fails.  For more details
              on hidden commands, see HIDDEN COMMANDS, below.

       slave hide exposedCmdName ?hiddenCmdName?
              This  command hides the exposed command exposedCmdName, renaming
              it to the hidden command hiddenCmdName, or keeping the same name
              if  the  argument  is not given, in the slave interpreter.  If a
              hidden command with the targeted name already exists, this  com-
              mand fails.  Currently both exposedCmdName and hiddenCmdName can
              not contain namespace qualifiers, or an error is  raised.   Com-
              mands to be hidden are looked up in the global namespace even if
              the current namespace is  not  the  global  one.  This  prevents
              slaves  from  fooling a master interpreter into hiding the wrong
              command, by making the current namespace be different  from  the
              global  one.   For  more  details on hidden commands, see HIDDEN
              COMMANDS, below.

       slave hidden
              Returns a list of the names of all hidden commands in slave.

       slave invokehidden ?-global hiddenName ?arg ..?
              This command invokes the hidden command hiddenName with the sup-
              plied  arguments,  in slave. No substitutions or evaluations are
              applied to the arguments.  If the -global  flag  is  given,  the
              command  is  invoked at the global level in the slave; otherwise
              it is invoked at the current call frame  and  can  access  local
              variables  in  that  or  outer call frames.  For more details on
              hidden commands, see HIDDEN COMMANDS, below.

       slave issafe
              Returns  1 if the slave interpreter is safe, 0 otherwise.

       slave marktrusted
              Marks the slave interpreter as trusted. Can only be invoked by a
              trusted  interpreter.  This  command  does not expose any hidden
              commands in the slave interpreter. The command has no effect  if
              the slave is already trusted.

       slave recursionlimit ?newlimit?
              Returns the maximum allowable nesting depth for the slave inter-
              preter.  If newlimit is specified, the recursion limit in  slave
              will  be  set  so  that  nesting  of more than newlimit calls to
              Tcl_Eval() and related procedures in slave will return an error.
              The newlimit value is also returned.  The newlimit value must be
              a positive integer between 1 and the maximum value of a non-long
              integer on the platform.

              The command sets the maximum size of the Tcl call stack only. It
              cannot by itself prevent stack overflows on the  C  stack  being
              used by the application. If your machine has a limit on the size
              of the C stack, you may get stack overflows before reaching  the
              limit  set  by  the  command. If this happens, see if there is a
              mechanism in your system for increasing the maximum size of  the
              C stack.

SAFE INTERPRETERS
       A  safe  interpreter  is  one with restricted functionality, so that is
       safe to execute an arbitrary script from your worst enemy without  fear
       of  that  script damaging the enclosing application or the rest of your
       computing environment.  In order to make an interpreter  safe,  certain
       commands  and variables are removed from the interpreter.  For example,
       commands to create files on disk are removed, and the exec  command  is
       removed,  since  it could be used to cause damage through subprocesses.
       Limited access to these facilities can be provided, by creating aliases
       to  the  master  interpreter  which check their arguments carefully and
       provide restricted access to a safe subset of facilities.  For example,
       file creation might be allowed in a particular subdirectory and subpro-
       cess invocation might be allowed for a carefully selected and fixed set
       of programs.

       A  safe  interpreter  is  created by specifying the -safe switch to the
       interp create command.  Furthermore, any slave created by a safe inter-
       preter will also be safe.

       A  safe interpreter is created with exactly the following set of built-
       in commands:

              after       append      array       binary
              break       case        catch       clock
              close       concat      continue    eof
              error       eval        expr        fblocked
              fcopy       fileevent   flush       for
              foreach     format      gets        global
              if          incr        info        interp
              join        lappend     lindex      linsert
              list        llength     lrange      lreplace
              lsearch     lsort       namespace   package
              pid         proc        puts        read
              regexp      regsub      rename      return
              scan        seek        set         split
              string      subst       switch      tell
              time        trace       unset       update
              uplevel     upvar       variable    vwait
              while

       The following commands are hidden by interp create when  it  creates  a
       safe interpreter:

              cd          encoding    exec        exit
              fconfigure  file        glob        load
              open        pwd         socket      source

       These  commands can be recreated later as Tcl procedures or aliases, or
       re-exposed by interp expose.

       The following commands from Tcl's library of support procedures are not
       present in a safe interpreter:

              auto_exec_ok    auto_import     auto_load
              auto_load_index auto_qualify    unknown

       Note  in particular that safe interpreters have no default unknown com-
       mand, so  Tcl's  default  autoloading  facilities  are  not  available.
       Autoload access to Tcl's commands that are normally autoloaded:

              auto_mkindex         auto_mkindex_old
              auto_reset           history
              parray               pkg_mkIndex
              ::pkg::create        ::safe::interpAddToAccessPath
              ::safe::interpCreate ::safe::interpConfigure
              ::safe::interpDelete ::safe::interpFindInAccessPath
              ::safe::interpInit   ::safe::setLogCmd
              tcl_endOfWord        tcl_findLibrary
              tcl_startOfNextWord  tcl_startOfPreviousWord
              tcl_wordBreakAfter   tcl_wordBreakBefore

       can  only  be  provided by explicit definition of an unknown command in
       the safe interpreter.  This will involve exposing the  source  command.
       This  is most easily accomplished by creating the safe interpreter with
       Tcl's Safe-Tcl mechanism.  Safe-Tcl provides safe versions  of  source,
       load,  and other Tcl commands needed to support autoloading of commands
       and the loading of packages.

       In addition, the env variable is not present in a safe interpreter,  so
       it  cannot share environment variables with other interpreters. The env
       variable poses a security  risk,  because  users  can  store  sensitive
       information  in  an  environment  variable. For example, the PGP manual
       recommends storing the PGP private key protection password in the envi-
       ronment  variable  PGPPASS. Making this variable available to untrusted
       code executing in a safe interpreter would incur a security risk.

       If extensions are  loaded  into  a  safe  interpreter,  they  may  also
       restrict  their  own  functionality to eliminate unsafe commands. For a
       discussion of management  of  extensions  for  safety  see  the  manual
       entries for Safe-Tcl and the load Tcl command.

       A  safe  interpreter  may  not  alter the recursion limit of any inter-
       preter, including itself.

ALIAS INVOCATION
       The alias mechanism has been carefully designed so that it can be  used
       safely  when  an  untrusted script is executing in a safe slave and the
       target of the alias is a trusted master.  The most important  thing  in
       guaranteeing safety is to ensure that information passed from the slave
       to the master is never evaluated or substituted in the master;  if this
       were  to  occur,  it would enable an evil script in the slave to invoke
       arbitrary functions in the master, which would compromise security.

       When the source for an alias is invoked in the slave  interpreter,  the
       usual Tcl substitutions are performed when parsing that command.  These
       substitutions are carried out in the source interpreter  just  as  they
       would  be  for any other command invoked in that interpreter.  The com-
       mand procedure for the source command takes its  arguments  and  merges
       them with the targetCmd and args for the alias to create a new array of
       arguments.  If the words of srcCmd were ``srcCmd arg1 arg2 ...  argN'',
       the  new set of words will be ``targetCmd arg arg ... arg arg1 arg2 ...
       argN'', where targetCmd and args are the values supplied when the alias
       was  created.   TargetCmd is then used to locate a command procedure in
       the target interpreter, and that command procedure is invoked with  the
       new  set  of  arguments.   An error occurs if there is no command named
       targetCmd in the target interpreter.  No additional  substitutions  are
       performed  on  the  words:   the  target  command  procedure is invoked
       directly, without going through the normal  Tcl  evaluation  mechanism.
       Substitutions  are  thus performed on each word exactly once: targetCmd
       and args were substituted when parsing the  command  that  created  the
       alias,  and arg1 - argN are substituted when the alias's source command
       is parsed in the source interpreter.

       When writing the targetCmds for aliases in  safe  interpreters,  it  is
       very important that the arguments to that command never be evaluated or
       substituted, since this would provide an escape mechanism  whereby  the
       slave  interpreter could execute arbitrary code in the master.  This in
       turn would compromise the security of the system.

HIDDEN COMMANDS
       Safe interpreters greatly restrict the functionality available  to  Tcl
       programs  executing within them.  Allowing the untrusted Tcl program to
       have direct access to this functionality is unsafe, because it  can  be
       used  for  a variety of attacks on the environment.  However, there are
       times when there is a legitimate need to use the dangerous  functional-
       ity  in  the  context of the safe interpreter. For example, sometimes a
       program must be sourced into the interpreter.  Another example  is  Tk,
       where  windows  are  bound  to  the hierarchy of windows for a specific
       interpreter; some potentially dangerous functions, e.g.  window manage-
       ment,  must  be  performed on these windows within the interpreter con-
       text.

       The interp command provides a solution to this problem in the  form  of
       hidden  commands.  Instead  of removing the dangerous commands entirely
       from a safe interpreter, these  commands  are  hidden  so  they  become
       unavailable  to Tcl scripts executing in the interpreter. However, such
       hidden commands can be invoked by any  trusted  ancestor  of  the  safe
       interpreter,  in  the  context  of  the  safe interpreter, using interp
       invoke. Hidden commands and exposed commands reside  in  separate  name
       spaces.  It  is possible to define a hidden command and an exposed com-
       mand by the same name within one interpreter.

       Hidden commands in a slave interpreter can be invoked in  the  body  of
       procedures  called  in the master during alias invocation. For example,
       an alias for source could be created in a slave interpreter. When it is
       invoked  in  the slave interpreter, a procedure is called in the master
       interpreter to check that the operation is allowable (e.g. it  asks  to
       source  a  file  that  the slave interpreter is allowed to access). The
       procedure then it invokes the hidden source command in the slave inter-
       preter  to  actually  source in the contents of the file. Note that two
       commands named source exist in the slave interpreter:  the  alias,  and
       the hidden command.

       Because  a  master  interpreter  may invoke a hidden command as part of
       handling an alias invocation, great care must be taken to avoid  evalu-
       ating any arguments passed in through the alias invocation.  Otherwise,
       malicious slave interpreters could cause a trusted  master  interpreter
       to execute dangerous commands on their behalf. See the section on ALIAS
       INVOCATION for a more complete discussion of this topic.  To help avoid
       this  problem, no substitutions or evaluations are applied to arguments
       of interp invokehidden.

       Safe interpreters are not allowed to invoke hidden  commands  in  them-
       selves  or in their descendants. This prevents safe slaves from gaining
       access to hidden functionality in themselves or their descendants.

       The set of hidden commands in an interpreter can be  manipulated  by  a
       trusted  interpreter  using  interp  expose and interp hide. The interp
       expose command moves a hidden command to the set of exposed commands in
       the interpreter identified by path, potentially renaming the command in
       the process. If an exposed command by the targeted name already exists,
       the operation fails. Similarly, interp hide moves an exposed command to
       the set of hidden commands in that interpreter. Safe  interpreters  are
       not allowed to move commands between the set of hidden and exposed com-
       mands, in either themselves or their descendants.

       Currently, the names of hidden commands cannot contain namespace quali-
       fiers, and you must first rename a command in a namespace to the global
       namespace before you can hide it.  Commands to be hidden by interp hide
       are  looked up in the global namespace even if the current namespace is
       not the global one. This prevents slaves from fooling a  master  inter-
       preter  into  hiding the wrong command, by making the current namespace
       be different from the global one.

CREDITS
       This mechanism is  based  on  the  Safe-Tcl  prototype  implemented  by
       Nathaniel Borenstein and Marshall Rose.

EXAMPLES
       Creating and using an alias for a command in the current interpreter:
              interp alias {} getIndex {} lsearch {alpha beta gamma delta}
              set idx [getIndex delta]

       Executing  an  arbitrary  command  in  a  safe  interpreter where every
       invokation of lappend is logged:
              set i [interp create -safe]
              interp hide $i lappend
              interp alias $i lappend {} loggedLappend $i
              proc loggedLappend {i args} {
                 puts "logged invokation of lappend $args"
                 # Be extremely careful about command construction
                 eval [linsert $args 0 \
                       interp invokehidden $i lappend]
              }
              interp eval $i $someUntrustedScript


SEE ALSO
       load(n), safe(n), Tcl_CreateSlave(3)


KEYWORDS
