info

Section: Tcl Built-In Commands (n)
Updated: 8.4
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NAME

info - Return information about the state of the Tcl interpreter  

SYNOPSIS

info option ?arg arg ...?

 

DESCRIPTION

This command provides information about various internals of the Tcl interpreter. The legal options (which may be abbreviated) are:

info args procname
Returns a list containing the names of the arguments to procedure procname, in order. Procname must be the name of a Tcl command procedure.
info body procname
Returns the body of procedure procname. Procname must be the name of a Tcl command procedure.
info class subcommand class ?arg ...
Returns information about the class, class. The subcommands are described in CLASS INTROSPECTION below.
info cmdcount
Returns a count of the total number of commands that have been invoked in this interpreter.
info commands ?pattern?
If pattern is not specified, returns a list of names of all the Tcl commands visible (i.e. executable without using a qualified name) to the current namespace, including both the built-in commands written in C and the command procedures defined using the proc command. If pattern is specified, only those names matching pattern are returned. Matching is determined using the same rules as for string match. pattern can be a qualified name like Foo::print*. That is, it may specify a particular namespace using a sequence of namespace names separated by double colons (::), and may have pattern matching special characters at the end to specify a set of commands in that namespace. If pattern is a qualified name, the resulting list of command names has each one qualified with the name of the specified namespace, and only the commands defined in the named namespace are returned.
info complete command
Returns 1 if command is a complete Tcl command in the sense of having no unclosed quotes, braces, brackets or array element names. If the command does not appear to be complete then 0 is returned. This command is typically used in line-oriented input environments to allow users to type in commands that span multiple lines; if the command is not complete, the script can delay evaluating it until additional lines have been typed to complete the command.
info coroutine
Returns the name of the currently executing coroutine, or the empty string if either no coroutine is currently executing, or the current coroutine has been deleted (but has not yet returned or yielded since deletion).
info default procname arg varname
Procname must be the name of a Tcl command procedure and arg must be the name of an argument to that procedure. If arg does not have a default value then the command returns 0. Otherwise it returns 1 and places the default value of arg into variable varname.
info errorstack ?interp?
Returns, in a form that is programmatically easy to parse, the function names and arguments at each level from the call stack of the last error in the given interp, or in the current one if not specified.

This form is an even-sized list alternating tokens and parameters. Tokens are currently either CALL, UP, or INNER, but other values may be introduced in the future. CALL indicates a procedure call, and its parameter is the corresponding info level 0. UP indicates a shift in variable frames generated by uplevel or similar, and applies to the previous CALL item. Its parameter is the level offset. INNER identifies the ``inner context'', which is the innermost atomic command or bytecode instruction that raised the error, along with its arguments when available. While CALL and UP allow to follow complex call paths, INNER homes in on the offending operation in the innermost procedure call, even going to sub-expression granularity.

This information is also present in the -errorstack entry of the options dictionary returned by 3-argument catch; info errorstack is a convenient way of retrieving it for uncaught errors at top-level in an interactive tclsh.

info exists varName
Returns 1 if the variable named varName exists in the current context (either as a global or local variable) and has been defined by being given a value, returns 0 otherwise.
info frame ?number?
This command provides access to all frames on the stack, even those hidden from info level. If number is not specified, this command returns a number giving the frame level of the command. This is 1 if the command is invoked at top-level. If number is specified, then the result is a dictionary containing the location information for the command at the numbered level on the stack.

If number is positive (> 0) then it selects a particular stack level (1 refers to the outer-most active command, 2 to the command it called, and so on, up to the current frame level which refers to info frame itself); otherwise it gives a level relative to the current command (0 refers to the current command, i.e., info frame itself, -1 to its caller, and so on).

This is similar to how info level works, except that this subcommand reports all frames, like sourced scripts, evals, uplevels, etc.

Note that for nested commands, like ``foo [bar [x]]'', only ``x'' will be seen by an info frame invoked within ``x''. This is the same as for info level and error stack traces.

The result dictionary may contain the keys listed below, with the specified meanings for their values:

type
This entry is always present and describes the nature of the location for the command. The recognized values are source, proc, eval, and precompiled.
source        
means that the command is found in a script loaded by the source command.
proc        
means that the command is found in dynamically created procedure body.
eval        
means that the command is executed by eval or uplevel.
precompiled        
means that the command is found in a pre-compiled script (loadable by the package tbcload), and no further information will be available.
line
This entry provides the number of the line the command is at inside of the script it is a part of. This information is not present for type precompiled. For type source this information is counted relative to the beginning of the file, whereas for the last two types the line is counted relative to the start of the script.
file
This entry is present only for type source. It provides the normalized path of the file the command is in.
cmd
This entry provides the string representation of the command. This is usually the unsubstituted form, however for commands which are a canonically-constructed list (e.g., as produced by the list command) executed by eval it is the substituted form as they have no other string representation. Care is taken that the canonicality property of the latter is not spoiled.
proc
This entry is present only if the command is found in the body of a regular Tcl procedure. It then provides the name of that procedure.
lambda
This entry is present only if the command is found in the body of an anonymous Tcl procedure, i.e. a lambda. It then provides the entire definition of the lambda in question.
level
This entry is present only if the queried frame has a corresponding frame returned by info level. It provides the index of this frame, relative to the current level (0 and negative numbers).

A thing of note is that for procedures statically defined in files the locations of commands in their bodies will be reported with type source and absolute line numbers, and not as type proc. The same is true for procedures nested in statically defined procedures, and literal eval scripts in files or statically defined procedures.

In contrast, procedure definitions and eval within a dynamically evaluated environment count line numbers relative to the start of their script, even if they would be able to count relative to the start of the outer dynamic script. That type of number usually makes more sense.

A different way of describing this behaviour is that file based locations are tracked as deeply as possible, and where this is not possible the lines are counted based on the smallest possible eval or procedure body, as that scope is usually easier to find than any dynamic outer scope.

The syntactic form {*} is handled like eval. I.e. if it is given a literal list argument the system tracks the line number within the list words as well, and otherwise all line numbers are counted relative to the start of each word (smallest scope)

info functions ?pattern?
If pattern is not specified, returns a list of all the math functions currently defined. If pattern is specified, only those functions whose name matches pattern are returned. Matching is determined using the same rules as for string match.
info globals ?pattern?
If pattern is not specified, returns a list of all the names of currently-defined global variables. Global variables are variables in the global namespace. If pattern is specified, only those names matching pattern are returned. Matching is determined using the same rules as for string match.
info hostname
Returns the name of the computer on which this invocation is being executed. Note that this name is not guaranteed to be the fully qualified domain name of the host. Where machines have several different names (as is common on systems with both TCP/IP (DNS) and NetBIOS-based networking installed,) it is the name that is suitable for TCP/IP networking that is returned.
info level ?number?
If number is not specified, this command returns a number giving the stack level of the invoking procedure, or 0 if the command is invoked at top-level. If number is specified, then the result is a list consisting of the name and arguments for the procedure call at level number on the stack. If number is positive then it selects a particular stack level (1 refers to the top-most active procedure, 2 to the procedure it called, and so on); otherwise it gives a level relative to the current level (0 refers to the current procedure, -1 to its caller, and so on). See the uplevel command for more information on what stack levels mean.
info library
Returns the name of the library directory in which standard Tcl scripts are stored. This is actually the value of the tcl_library variable and may be changed by setting tcl_library.
info loaded ?interp?
Returns a list describing all of the packages that have been loaded into interp with the load command. Each list element is a sub-list with two elements consisting of the name of the file from which the package was loaded and the name of the package. For statically-loaded packages the file name will be an empty string. If interp is omitted then information is returned for all packages loaded in any interpreter in the process. To get a list of just the packages in the current interpreter, specify an empty string for the interp argument.
info locals ?pattern?
If pattern is not specified, returns a list of all the names of currently-defined local variables, including arguments to the current procedure, if any. Variables defined with the global, upvar and variable commands will not be returned. If pattern is specified, only those names matching pattern are returned. Matching is determined using the same rules as for string match.
info nameofexecutable
Returns the full path name of the binary file from which the application was invoked. If Tcl was unable to identify the file, then an empty string is returned.
info object subcommand object ?arg ...
Returns information about the object, object. The subcommands are described in OBJECT INTROSPECTION below.
info patchlevel
Returns the value of the global variable tcl_patchLevel, which holds the exact version of the Tcl library by default.
info procs ?pattern?
If pattern is not specified, returns a list of all the names of Tcl command procedures in the current namespace. If pattern is specified, only those procedure names in the current namespace matching pattern are returned. Matching is determined using the same rules as for string match. If pattern contains any namespace separators, they are used to select a namespace relative to the current namespace (or relative to the global namespace if pattern starts with ::) to match within; the matching pattern is taken to be the part after the last namespace separator.
info script ?filename?
If a Tcl script file is currently being evaluated (i.e. there is a call to Tcl_EvalFile active or there is an active invocation of the source command), then this command returns the name of the innermost file being processed. If filename is specified, then the return value of this command will be modified for the duration of the active invocation to return that name. This is useful in virtual file system applications. Otherwise the command returns an empty string.
info sharedlibextension
Returns the extension used on this platform for the names of files containing shared libraries (for example, .so under Solaris). If shared libraries are not supported on this platform then an empty string is returned.
info tclversion
Returns the value of the global variable tcl_version, which holds the major and minor version of the Tcl library by default.
info vars ?pattern?
If pattern is not specified, returns a list of all the names of currently-visible variables. This includes locals and currently-visible globals. If pattern is specified, only those names matching pattern are returned. Matching is determined using the same rules as for string match. pattern can be a qualified name like Foo::option*. That is, it may specify a particular namespace using a sequence of namespace names separated by double colons (::), and may have pattern matching special characters at the end to specify a set of variables in that namespace. If pattern is a qualified name, the resulting list of variable names has each matching namespace variable qualified with the name of its namespace. Note that a currently-visible variable may not yet ``exist'' if it has not been set (e.g. a variable declared but not set by variable).
 

CLASS INTROSPECTION

The following subcommand values are supported by info class:

info class call class method
Returns a description of the method implementations that are used to provide a stereotypical instance of class's implementation of method (stereotypical instances being objects instantiated by a class without having any object-specific definitions added). This consists of a list of lists of four elements, where each sublist consists of a word that describes the general type of method implementation (being one of method for an ordinary method, filter for an applied filter, and unknown for a method that is invoked as part of unknown method handling), a word giving the name of the particular method invoked (which is always the same as method for the method type, and ``unknown'' for the unknown type), a word giving the fully qualified name of the class that defined the method, and a word describing the type of method implementation (see info class methodtype).

Note that there is no inspection of whether the method implementations actually use next to transfer control along the call chain.

info class constructor class
This subcommand returns a description of the definition of the constructor of class class. The definition is described as a two element list; the first element is the list of arguments to the constructor in a form suitable for passing to another call to proc or a method definition, and the second element is the body of the constructor. If no constructor is present, this returns the empty list.
info class definition class method
This subcommand returns a description of the definition of the method named method of class class. The definition is described as a two element list; the first element is the list of arguments to the method in a form suitable for passing to another call to proc or a method definition, and the second element is the body of the method.
info class destructor class
This subcommand returns the body of the destructor of class class. If no destructor is present, this returns the empty string.
info class filters class
This subcommand returns the list of filter methods set on the class.
info class forward class method
This subcommand returns the argument list for the method forwarding called method that is set on the class called class.
info class instances class ?pattern?
This subcommand returns a list of instances of class class. If the optional pattern argument is present, it constrains the list of returned instances to those that match it according to the rules of string match.
info class methods class ?options...?
This subcommand returns a list of all public (i.e. exported) methods of the class called class. Any of the following options may be specified, controlling exactly which method names are returned:
-all
If the -all flag is given, the list of methods will include those methods defined not just by the class, but also by the class's superclasses and mixins.
-private
If the -private flag is given, the list of methods will also include the private (i.e. non-exported) methods of the class (and superclasses and mixins, if -all is also given).
info class methodtype class method
This subcommand returns a description of the type of implementation used for the method named method of class class. When the result is method, further information can be discovered with info class definition, and when the result is forward, further information can be discovered with info class forward.
info class mixins class
This subcommand returns a list of all classes that have been mixed into the class named class.
info class subclasses class ?pattern?
This subcommand returns a list of direct subclasses of class class. If the optional pattern argument is present, it constrains the list of returned classes to those that match it according to the rules of string match.
info class superclasses class
This subcommand returns a list of direct superclasses of class class in inheritance precedence order.
info class variables class
This subcommand returns a list of all variables that have been declared for the class named class (i.e. that are automatically present in the class's methods, constructor and destructor).
 

OBJECT INTROSPECTION

The following subcommand values are supported by info object:

info object call object method
Returns a description of the method implementations that are used to provide object's implementation of method. This consists of a list of lists of four elements, where each sublist consists of a word that describes the general type of method implementation (being one of method for an ordinary method, filter for an applied filter, and unknown for a method that is invoked as part of unknown method handling), a word giving the name of the particular method invoked (which is always the same as method for the method type, and ``unknown'' for the unknown type), a word giving what defined the method (the fully qualified name of the class, or the literal string object if the method implementation is on an instance), and a word describing the type of method implementation (see info object methodtype).

Note that there is no inspection of whether the method implementations actually use next to transfer control along the call chain.

info object class object ?className?
If className is unspecified, this subcommand returns class of the object object. If className is present, this subcommand returns a boolean value indicating whether the object is of that class.
info object definition object method
This subcommand returns a description of the definition of the method named method of object object. The definition is described as a two element list; the first element is the list of arguments to the method in a form suitable for passing to another call to proc or a method definition, and the second element is the body of the method.
info object filters object
This subcommand returns the list of filter methods set on the object.
info object forward object method
This subcommand returns the argument list for the method forwarding called method that is set on the object called object.
info object isa category object ?arg?
This subcommand tests whether an object belongs to a particular category, returning a boolean value that indicates whether the object argument meets the criteria for the category. The supported categories are:
info object isa class object
This returns whether object is a class (i.e. an instance of oo::class or one of its subclasses).
info object isa metaclass object
This returns whether object is a class that can manufacture classes (i.e. is oo::class or a subclass of it).
info object isa mixin object class
This returns whether class is directly mixed into object.
info object isa object object
This returns whether object really is an object.
info object isa typeof object class
This returns whether class is the type of object (i.e. whether object is an instance of class or one of its subclasses, whether direct or indirect).
info object methods object ?option...?
This subcommand returns a list of all public (i.e. exported) methods of the object called object. Any of the following options may be specified, controlling exactly which method names are returned:
-all
If the -all flag is given, the list of methods will include those methods defined not just by the object, but also by the object's class and mixins, plus the superclasses of those classes.
-private
If the -private flag is given, the list of methods will also include the private (i.e. non-exported) methods of the object (and classes, if -all is also given).
info object methodtype object method
This subcommand returns a description of the type of implementation used for the method named method of object object. When the result is method, further information can be discovered with info object definition, and when the result is forward, further information can be discovered with info object forward.
info object mixins object
This subcommand returns a list of all classes that have been mixed into the object named object.
info object namespace object
This subcommand returns the name of the internal namespace of the object named object.
info object variables object
This subcommand returns a list of all variables that have been declared for the object named object (i.e. that are automatically present in the object's methods).
info object vars object ?pattern?
This subcommand returns a list of all variables in the private namespace of the object named object. If the optional pattern argument is given, it is a filter (in the syntax of a string match glob pattern) that constrains the list of variables returned. Note that this is different from the list returned by info object variables; that can include variables that are currently unset, whereas this can include variables that are not automatically included by any of object's methods (or those of its class, superclasses or mixins).
 

EXAMPLES

This command prints out a procedure suitable for saving in a Tcl script: 


proc printProc {procName} {
    set result [list proc $procName]
    set formals {}
    foreach var [info args $procName] {
        if {[info default $procName $var def]} {
            lappend formals [list $var $def]
        } else {
            # Still need the list-quoting because variable
            # names may properly contain spaces.
            lappend formals [list $var]
        }
    }
    puts [lappend result $formals [info body $procName]]
}
 

EXAMPLES WITH OBJECTS

Every object necessarily knows what its class is; this information is trivially extractable through introspection: 


oo::class create c
c create o
puts [info object class o]
                     → prints "::c"
puts [info object class c]
                     → prints "::oo::class"

The introspection capabilities can be used to discover what class implements a method and get how it is defined. This procedure illustrates how: 


proc getDef {obj method} {
    foreach inf [info object call $obj $method] {
        lassign $inf calltype name locus methodtype
        # Assume no forwards or filters, and hence no $calltype
        # or $methodtype checks...
        if {$locus eq "object"} {
            return [info object definition $obj $name]
        } else {
            return [info class definition $locus $name]
        }
    }
    error "no definition for $method"
}

This is an alternate way of looking up the definition; it is implemented by manually scanning the list of methods up the inheritance tree. This code assumes that only single inheritance is in use, and that there is no complex use of mixed-in classes (in such cases, using info object call as above is the simplest way of doing this by far): 


proc getDef {obj method} {
    if {$method in [info object methods $obj]} {
        # Assume no forwards
        return [info object definition $obj $method]
    }
    set cls [info object class $obj]
    while {$method ni [info class methods $cls]} {
        # Assume the simple case
        set cls [lindex [info class superclass $cls] 0]
        if {$cls eq ""} {
            error "no definition for $method"
        }
    }
    # Assume no forwards
    return [info class definition $cls $method]
}
 

SEE ALSO

global(n), oo::class(n), oo::define(n), oo::object(n), proc(n), self(n), tcl_library(n), tcl_patchLevel(n), tcl_version(n)  

KEYWORDS

command, information, interpreter, introspection, level, namespace, object, procedure, variable

 

Index

NAME
SYNOPSIS
DESCRIPTION
CLASS INTROSPECTION
OBJECT INTROSPECTION
EXAMPLES
EXAMPLES WITH OBJECTS
SEE ALSO
KEYWORDS