Windows PowerShell command on Get-command interp

Manual Pages for UNIX Operating System command usage for man interp

Tcl Built-In Commands interp(1T)

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NAME

interp - Create and manipulate Tcl interpreters

SYNOPSIS

interp option ?arg arg ...?

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DESCRIPTION

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 master and the new interpreter is called a slave. A mas-

ter 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 vari-

ables. A master interpreter may create connections between

its slaves and itself using a mechanism called an alias. An

alias is a command in a slave interpreter which, when

invoked, causes a command to be invoked in its master inter-

preter or in another slave interpreter. The only other con-

nections between interpreters are through environment vari-

ables (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 com-

mand) 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 inter-

preters. 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 inter-

preters or the application's environment. For example, all

IO channel creation commands and subprocess creation com-

mands are made inaccessible to safe interpreters. 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 |

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 | 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. Tcl Last change: 7.6 1

Tcl Built-In Commands interp(1T)

A qualified interpreter name is a proper Tcl lists contain-

ing 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 evaluated 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

identified 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 com-

mand, 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 ele-

ments 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 Tcl Last change: 7.6 2

Tcl Built-In Commands interp(1T)

command, which will be created in the source inter-

preter. TargetPath and targetCmd specify a target

interpreter and command, and the arg arguments, if any,

specify additional arguments to targetCmd which are prepended to any arguments 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 tar-

get 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 com-

mand 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 inter-

preter 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 com-

mands).

interp create ?-safe? ?--? ?path?

Creates a slave interpreter identified by path and a

new command, 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 identi-

fied 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; oth-

erwise the slave will include the full set of Tcl

built-in commands and variables. 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.

Tcl Last change: 7.6 3

Tcl Built-In Commands interp(1T)

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 execute 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 command with the tar- |

geted name already exists, this command fails. Hidden |

commands are explained in more detail in HIDDEN COM- |

MANDS, below. |

interp hide path exposedCmdName ?hiddenCmdName? ||

Makes the exposed command exposedCmdName hidden, renam- |

ing 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 hiding the wrong command, by |

making the current namespace be different from the glo- |

bal one. Hidden commands are explained in more detail | Tcl Last change: 7.6 4

Tcl Built-In Commands interp(1T)

in HIDDEN COMMANDS, below. |

interp hidden path ||

Returns a list of the names of all hidden commands in |

the interpreter identified by path. |

interp invokehidden path ?- |

global? hiddenCmdName ?arg ...? | |

Invokes the hidden command hiddenCmdName with the argu- |

ments supplied in the interpreter denoted by path. No |

substitutions or evaluation are applied to the argu- |

ments. If the -global flag is present, the hidden com- |

mand 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 speci-

fied 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 com- |

mand 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 speci-

fied, 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 plat-

form. 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 mechan-

ism 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

Tcl Last change: 7.6 5

Tcl Built-In Commands interp(1T)

and the interpreter identified by destPath. Both inter-

preters 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 des-

troyed.

interp slaves ?path?

Returns a Tcl list of the names of all the slave inter-

preters 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 inter-

preter path and source command name, just as in interp

alias above. The name of the target interpreter is

returned as an interpreter path, relative to the invok-

ing 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

available 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 determine the exact behavior of the command. The valid forms of this command 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 com-

mands). slave alias srcToken Returns a Tcl list whose elements are the targetCmd and args associated with the alias represented by srcToken Tcl Last change: 7.6 6

Tcl Built-In Commands interp(1T)

(this is the value returned when the alias was created; it is possible that the actual source command in the slave is different from srcToken). slave alias srcToken {}

Deletes the alias for srcToken in the slave inter-

preter. srcToken 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 current context stack frame of slave; this is so that the

implementations (in a master interpreter) of aliases in

a slave interpreter can execute scripts in the slave

that find out information 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 targeted 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 command fails. | Currently both exposedCmdName and hiddenCmdName can not | contain namespace qualifiers, or an error is raised. | Tcl Last change: 7.6 7

Tcl Built-In Commands interp(1T)

Commands to be hidden are looked up in the global |

namespace even if the current namespace is not the glo- |

bal 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 COM- |

MANDS, 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 supplied arguments, in slave. No substitutions or |

evaluations are applied to the arguments. If the -glo- |

bal 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 other-

wise. 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 interpreter. 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 pro-

cedures 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 mechan-

ism in your system for increasing the maximum size of the C stack. Tcl Last change: 7.6 8

Tcl Built-In Commands interp(1T)

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 inter-

preter which check their arguments carefully and provide

restricted access to a safe subset of facilities. For exam-

ple, file creation might be allowed in a particular sub-

directory and subprocess 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 interpreter 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. |

Tcl Last change: 7.6 9

Tcl Built-In Commands interp(1T)

The following commands from Tcl's library of support pro- |

cedures 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 command, 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 environ-

ment variable. For example, the PGP manual recommends stor-

ing the PGP private key protection password in the environ-

ment 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

interpreter, including itself.

ALIAS INVOCATION Tcl Last change: 7.6 10

Tcl Built-In Commands interp(1T)

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 mas-

ter. 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 inter-

preter, the usual Tcl substitutions are performed when pars-

ing 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 command 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 ``tar-

getCmd 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 inter-

preters, 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 avail- |

able to Tcl programs executing within them. Allowing the |

untrusted Tcl program to have direct access to this func- |

tionality 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 poten- |

tially dangerous functions, e.g. window management, must be | Tcl Last change: 7.6 11

Tcl Built-In Commands interp(1T)

performed on these windows within the interpreter context. |

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 command 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 invoca- |

tion. For example, an alias for source could be created in a |

slave interpreter. When it is invoked in the slave inter- |

preter, 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 interpreter 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 evaluating any arguments passed in through |

the alias invocation. Otherwise, malicious slave inter- |

preters 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 themselves or in their descendants. This prevents safe |

slaves from gaining access to hidden functionality in them- |

selves or their descendants. |

The set of hidden commands in an interpreter can be manipu- |

lated by a trusted interpreter using interp expose and |

interp hide. The interp expose command moves a hidden com- |

mand to the set of exposed commands in the interpreter iden- |

tified by path, potentially renaming the command in the pro- |

cess. 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 inter- |

preter. Safe interpreters are not allowed to move commands |

between the set of hidden and exposed commands, in either | Tcl Last change: 7.6 12

Tcl Built-In Commands interp(1T)

themselves or their descendants. | Currently, the names of hidden commands cannot contain | namespace qualifiers, 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 |

interpreter 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 imple-

mented 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

alias, master interpreter, safe interpreter, slave inter-

preter

ATTRIBUTES

See attributes(5) for descriptions of the following attri-

butes: Tcl Last change: 7.6 13

Tcl Built-In Commands interp(1T)

_______________________________________

| ATTRIBUTE TYPE | ATTRIBUTE VALUE|

|____________________|__________________|_

| Availability | runtime/tcl-8 |

|____________________|__________________|_

| Interface Stability| Uncommitted |

|____________________|_________________|

NOTES Source for Tcl is available on http://opensolaris.org. Tcl Last change: 7.6 14