Lua debug standard library

Version: stable

FUNCTIONS
debug.debug() enters interactive debugging
debug.getfenv() returns the environment of an object
debug.gethook() returns the current hook settings
debug.getinfo() returns a table with information about a function
debug.getlocal() returns name and value of a local variable
debug.getmetatable() returns the metatable of the given object
debug.getregistry() returns the registry table
debug.getupvalue() returns the name and value of an upvalue
debug.setfenv() sets the environment of an object
debug.sethook() sets a debug hook function
debug.setlocal() sets the value of the local variable
debug.setmetatable() sets the metatable for an object
debug.setupvalue() sets an upvalue for a function
debug.traceback() returns a string with a traceback of the stack call

Functions

debug.debug()

debug.debug()

Enters an interactive mode with the user, running each string that the user enters. Using simple commands and other debug facilities, the user can inspect global and local variables, change their values, evaluate expressions, and so on. A line containing only the word cont finishes this function, so that the caller continues its execution. Note that commands for debug.debug are not lexically nested within any function, and so have no direct access to local variables.

PARAMETERS

None

debug.getfenv()

debug.getfenv(o)

Returns the environment of object o.

PARAMETERS

o

debug.gethook()

debug.gethook([thread])

Returns the current hook settings of the thread, as three values: the current hook function, the current hook mask, and the current hook count (as set by the debug.sethook function).

PARAMETERS

[thread]

debug.getinfo()

debug.getinfo([thread],function,[what])

Returns a table with information about a function. You can give the function directly, or you can give a number as the value of function, which means the function running at level function of the call stack of the given thread: level 0 is the current function (getinfo itself); level 1 is the function that called getinfo; and so on. If function is a number larger than the number of active functions, then getinfo returns nil. The returned table can contain all the fields returned by lua_getinfo, with the string what describing which fields to fill in. The default for what is to get all information available, except the table of valid lines. If present, the option 'f' adds a field named func with the function itself. If present, the option 'L' adds a field named activelines with the table of valid lines. For instance, the expression debug.getinfo(1,"n").name returns a table with a name for the current function, if a reasonable name can be found, and the expression debug.getinfo(print) returns a table with all available information about the print function.

PARAMETERS

[thread]
function
[what]

debug.getlocal()

debug.getlocal([thread],level,local)

This function returns the name and the value of the local variable with index local of the function at level level of the stack. (The first parameter or local variable has index 1, and so on, until the last active local variable.) The function returns nil if there is no local variable with the given index, and raises an error when called with a level out of range. (You can call debug.getinfo to check whether the level is valid.) Variable names starting with '(' (open parentheses) represent internal variables (loop control variables, temporaries, and C function locals).

PARAMETERS

[thread]
level
local

debug.getmetatable()

debug.getmetatable(object)

Returns the metatable of the given object or nil if it does not have a metatable.

PARAMETERS

object

debug.getregistry()

debug.getregistry()

Returns the registry table .

PARAMETERS

None

debug.getupvalue()

debug.getupvalue(func,up)

This function returns the name and the value of the upvalue with index up of the function func. The function returns nil if there is no upvalue with the given index.

PARAMETERS

func
up

debug.setfenv()

debug.setfenv(object,table)

Sets the environment of the given object to the given table. Returns object.

PARAMETERS

object
table

debug.sethook()

debug.sethook([thread],hook,mask,[count])

Sets the given function as a hook. The string mask and the number count describe when the hook will be called. The string mask may have the following characters, with the given meaning:

"c"
the hook is called every time Lua calls a function;
"r"
the hook is called every time Lua returns from a function;
"l"
the hook is called every time Lua enters a new line of code.
With a count different from zero, the hook is called after every count instructions. When called without arguments, debug.sethook turns off the hook. When the hook is called, its first parameter is a string describing the event that has triggered its call: "call", "return" (or "tail return", when simulating a return from a tail call), "line", and "count". For line events, the hook also gets the new line number as its second parameter. Inside a hook, you can call getinfo with level 2 to get more information about the running function (level 0 is the getinfo function, and level 1 is the hook function), unless the event is "tail return". In this case, Lua is only simulating the return, and a call to getinfo will return invalid data.

PARAMETERS

[thread]
hook
mask
[count]

debug.setlocal()

debug.setlocal([thread],level,local,value)

This function assigns the value value to the local variable with index local of the function at level level of the stack. The function returns nil if there is no local variable with the given index, and raises an error when called with a level out of range. (You can call getinfo to check whether the level is valid.) Otherwise, it returns the name of the local variable.

PARAMETERS

[thread]
level
local
value

debug.setmetatable()

debug.setmetatable(object,table)

Sets the metatable for the given object to the given table (which can be nil).

PARAMETERS

object
table

debug.setupvalue()

debug.setupvalue(func,up,value)

This function assigns the value value to the upvalue with index up of the function func. The function returns nil if there is no upvalue with the given index. Otherwise, it returns the name of the upvalue.

PARAMETERS

func
up
value

debug.traceback()

debug.traceback([thread],[message],[level])

Returns a string with a traceback of the call stack. An optional message string is appended at the beginning of the traceback. An optional level number tells at which level to start the traceback (default is 1, the function calling traceback).

PARAMETERS

[thread]
[message]
[level]