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'\"
'\" Copyright (c) 1995-1996 Sun Microsystems, Inc.
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'\" RCS: @(#) $Id: interp.n,v 1.8 2002/03/07 20:17:22 dgp Exp $
'\" 
.so man.macros
.TH interp n 7.6 Tcl "Tcl Built-In Commands"
.BS
'\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
interp \- Create and manipulate Tcl interpreters
.SH SYNOPSIS
\fBinterp \fIoption \fR?\fIarg arg ...\fR?
.BE

.SH DESCRIPTION
.PP
This command makes it possible to create one or more new Tcl 
interpreters that co-exist with the creating interpreter in the
same application.  The creating interpreter is called the \fImaster\fR
and the new interpreter is called a \fIslave\fR. 
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.
.PP
Each interpreter is independent from the others: it has its own name
space for commands, procedures, and global variables.
A master interpreter may create connections between its slaves and
itself using a mechanism called an \fIalias\fR.  An \fIalias\fR is
a command in a slave interpreter which, when invoked, causes a
command to be invoked in its master interpreter or in another slave
interpreter.  The only other connections between interpreters are
through environment variables (the \fBenv\fR 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 \fBopen\fR command)
is no longer shared between interpreters. Explicit commands are provided to
share files and to transfer references to open files from one interpreter
to another.
.PP
The \fBinterp\fR command also provides support for \fIsafe\fR
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 damaging other interpreters or the
application's environment. For example, all IO channel creation
commands and subprocess creation commands are made inaccessible to safe
interpreters.
.VS
See SAFE INTERPRETERS below for more information on
what features are present in a safe interpreter.
The dangerous functionality is not removed from the safe interpreter;
instead, it is \fIhidden\fR, 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 protected 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.
.VE
.PP
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 \fBa\fR is a slave of
the current interpreter and it has a slave \fBa1\fR, which in turn has a
slave \fBa11\fR, the qualified name of \fBa11\fR in \fBa\fR is the list
\fBa1 a11\fR.
.PP
The \fBinterp\fR command, described below, accepts qualified interpreter
names as arguments; the interpreter in which the command is being evaluated
can always be referred to as \fB{}\fR (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.

.VS
.SH "THE INTERP COMMAND"
.PP
.VE
The \fBinterp\fR 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 \fIoption\fR argument:
.TP
\fBinterp\fR \fBalias\fR \fIsrcPath\fR \fIsrcCmd\fR
Returns a Tcl list whose elements are the \fItargetCmd\fR and
\fIarg\fRs associated with the alias named \fIsrcCmd\fR
(all of these are the values specified when the alias was
created; it is possible that the actual source command in the
slave is different from \fIsrcCmd\fR if it was renamed).
.TP
\fBinterp\fR \fBalias\fR \fIsrcPath\fR \fIsrcCmd\fR \fB{}\fR
Deletes the alias for \fIsrcCmd\fR in the slave interpreter identified by
\fIsrcPath\fR.
\fIsrcCmd\fR refers to the name under which the alias
was created;  if the source command has been renamed, the renamed
command will be deleted.
.TP
\fBinterp\fR \fBalias\fR \fIsrcPath\fR \fIsrcCmd\fR \fItargetPath\fR \fItargetCmd \fR?\fIarg arg ...\fR?
This command creates an alias between one slave and another (see the
\fBalias\fR 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.
\fISrcPath\fR and \fIsrcCmd\fR identify the source of the alias.
\fISrcPath\fR is a Tcl list whose elements select a particular
interpreter.  For example, ``\fBa b\fR'' identifies an interpreter
\fBb\fR, which is a slave of interpreter \fBa\fR, which is a slave
of the invoking interpreter.  An empty list specifies the interpreter
invoking the command.  \fIsrcCmd\fR gives the name of a new
command, which will be created in the source interpreter.
\fITargetPath\fR and \fItargetCmd\fR specify a target interpreter
and command, and the \fIarg\fR arguments, if any, specify additional
arguments to \fItargetCmd\fR which are prepended to any arguments specified
in the invocation of \fIsrcCmd\fR.
\fITargetCmd\fR 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.
.TP
\fBinterp\fR \fBaliases \fR?\fIpath\fR?
This command returns a Tcl list of the names of all the source commands for
aliases defined in the interpreter identified by \fIpath\fR.
.TP
\fBinterp\fR \fBcreate \fR?\fB\-safe\fR? ?\fB\-\|\-\fR? ?\fIpath\fR?
Creates a slave interpreter identified by \fIpath\fR and a new command,
called a \fIslave command\fR. The name of the slave command is the last
component of \fIpath\fR. The new slave interpreter and the slave command
are created in the interpreter identified by the path obtained by removing
the last component from \fIpath\fR. For example, if \fIpath is \fBa b
c\fR then a new slave interpreter and slave command named \fBc\fR are
created in the interpreter identified by the path \fBa b\fR.
The slave command may be used to manipulate the new interpreter as
described below. If \fIpath\fR is omitted, Tcl creates a unique name of the
form \fBinterp\fIx\fR, where \fIx\fR is an integer, and uses it for the
interpreter and the slave command. If the \fB\-safe\fR 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 variables. The \fB\-\|\-\fR switch can be used to
mark the end of switches;  it may be needed if \fIpath\fR is an unusual
value such as \fB\-safe\fR. 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.
.TP
\fBinterp\fR \fBdelete \fR?\fIpath ...?\fR
Deletes zero or more interpreters given by the optional \fIpath\fR
arguments, and for each interpreter, it also deletes its slaves. The
command also deletes the slave command for each interpreter deleted.
For each \fIpath\fR argument, if no interpreter by that name
exists, the command raises an error.
.TP
\fBinterp\fR \fBeval\fR \fIpath arg \fR?\fIarg ...\fR?
This command concatenates all of the \fIarg\fR arguments in the same
fashion as the \fBconcat\fR command, then evaluates the resulting string as
a Tcl script in the slave interpreter identified by \fIpath\fR. The result
of this evaluation (including error information such as the \fBerrorInfo\fR
and \fBerrorCode\fR variables, if an error occurs) is returned to the
invoking interpreter.
.TP
\fBinterp exists \fIpath\fR
Returns  \fB1\fR if a slave interpreter by the specified \fIpath\fR
exists in this master, \fB0\fR otherwise. If \fIpath\fR is omitted, the
invoking interpreter is used.
.VS "" BR
.TP
\fBinterp expose \fIpath\fR \fIhiddenName\fR ?\fIexposedCmdName\fR?
Makes the hidden command \fIhiddenName\fR exposed, eventually bringing
it back under a new \fIexposedCmdName\fR name (this name is currently
accepted only if it is a valid global name space name without any ::),
in the interpreter
denoted by \fIpath\fR.
If an exposed command with the targetted name already exists, this command
fails.
Hidden commands are explained in more detail in HIDDEN COMMANDS, below.
.TP
\fBinterp\fR \fBhide\fR \fIpath\fR \fIexposedCmdName\fR ?\fIhiddenCmdName\fR?
Makes the exposed command \fIexposedCmdName\fR hidden, renaming
it to the hidden command \fIhiddenCmdName\fR, or keeping the same name if
\fIhiddenCmdName\fR is not given, in the interpreter denoted 
by \fIpath\fR.
If a hidden command with the targetted name already exists, this command
fails.
Currently both \fIexposedCmdName\fR and \fIhiddenCmdName\fR can 
not contain namespace qualifiers, or an error is raised.
Commands to be hidden by \fBinterp hide\fR 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.
Hidden commands are explained in more detail in HIDDEN COMMANDS, below.
.TP
\fBinterp\fR \fBhidden\fR \fIpath\fR
Returns a list of the names of all hidden commands in the interpreter
identified by \fIpath\fR.
.TP
\fBinterp\fR \fBinvokehidden\fR \fIpath\fR ?\fB-global\fR? \fIhiddenCmdName\fR ?\fIarg ...\fR?
Invokes the hidden command \fIhiddenCmdName\fR with the arguments supplied
in the interpreter denoted by \fIpath\fR. No substitutions or evaluation
are applied to the arguments.
If the \fB-global\fR 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.
.VE
.TP
\fBinterp issafe\fR ?\fIpath\fR?
Returns \fB1\fR if the interpreter identified by the specified \fIpath\fR
is safe, \fB0\fR otherwise.
.VS "" BR
.TP
\fBinterp marktrusted\fR \fIpath\fR
Marks the interpreter identified by \fIpath\fR 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 \fIpath\fR is
already trusted.
.VE
.TP
\fBinterp\fR \fBrecursionlimit\fR \fIpath\fR ?\fInewlimit\fR?
Returns the maximum allowable nesting depth for the interpreter
specified by \fIpath\fR.  If \fInewlimit\fR is specified,
the interpreter recursion limit will be set so that nesting
of more than \fInewlimit\fR calls to \fBTcl_Eval()\fR
and related procedures in that interpreter will return an error.
The \fInewlimit\fR value is also returned.
The \fInewlimit\fR value must be a positive integer between 1 and the
maximum value of a non-long integer on the platform.  
.sp
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. 
.TP
\fBinterp\fR \fBshare\fR \fIsrcPath channelId destPath\fR
Causes the IO channel identified by \fIchannelId\fR to become shared
between the interpreter identified by \fIsrcPath\fR and the interpreter
identified by \fIdestPath\fR. 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.
.TP
\fBinterp\fR \fBslaves\fR ?\fIpath\fR?
Returns a Tcl list of the names of all the slave interpreters associated
with the interpreter identified by \fIpath\fR. If \fIpath\fR is omitted,
the invoking interpreter is used.
.TP
\fBinterp\fR \fBtarget\fR \fIpath alias\fR
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 \fBinterp alias\fR above. The name of the target interpreter is
returned as an interpreter path, relative 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.
.TP
\fBinterp\fR \fBtransfer\fR \fIsrcPath channelId destPath\fR
Causes the IO channel identified by \fIchannelId\fR to become available in
the interpreter identified by \fIdestPath\fR and unavailable in the
interpreter identified by \fIsrcPath\fR.

.SH "SLAVE COMMAND"
.PP
For each slave interpreter created with the \fBinterp\fR 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:
.CS
\fIslave command \fR?\fIarg arg ...\fR?
.CE
\fISlave\fR is the name of the interpreter, and \fIcommand\fR
and the \fIarg\fRs determine the exact behavior of the command.
The valid forms of this command are:
.TP
\fIslave \fBaliases\fR
Returns a Tcl list whose elements are the names of all the
aliases in \fIslave\fR.  The names returned are the \fIsrcCmd\fR
values used when the aliases were created (which may not be the same
as the current names of the commands, if they have been
renamed).
.TP
\fIslave \fBalias \fIsrcCmd\fR
Returns a Tcl list whose elements are the \fItargetCmd\fR and
\fIarg\fRs associated with the alias named \fIsrcCmd\fR
(all of these are the values specified when the alias was
created; it is possible that the actual source command in the
slave is different from \fIsrcCmd\fR if it was renamed).
.TP
\fIslave \fBalias \fIsrcCmd \fB{}\fR
Deletes the alias for \fIsrcCmd\fR in the slave interpreter.
\fIsrcCmd\fR refers to the name under which the alias
was created;  if the source command has been renamed, the renamed
command will be deleted.
.TP
\fIslave \fBalias \fIsrcCmd targetCmd \fR?\fIarg ..\fR?
Creates an alias such that whenever \fIsrcCmd\fR is invoked
in \fIslave\fR, \fItargetCmd\fR is invoked in the master.
The \fIarg\fR arguments will be passed to \fItargetCmd\fR as additional
arguments, prepended before any arguments passed in the invocation of
\fIsrcCmd\fR.
See ALIAS INVOCATION below for details.
.TP
\fIslave \fBeval \fIarg \fR?\fIarg ..\fR?
This command concatenates all of the \fIarg\fR arguments in