erlang

erlang

The Erlang BIFs

By convention, most built-in functions (BIFs) are seen as being in the module erlang. A number of the BIFs are viewed more or less as part of the Erlang programming language and are auto-imported. Thus, it is not necessary to specify the module name and both the calls atom_to_list(Erlang) and erlang:atom_to_list(Erlang) are identical.

In the text, auto-imported BIFs are listed without module prefix. BIFs listed with module prefix are not auto-imported.

BIFs may fail for a variety of reasons. All BIFs fail with reason badarg if they are called with arguments of an incorrect type. The other reasons that may make BIFs fail are described in connection with the description of each individual BIF.

Some BIFs may be used in guard tests, these are marked with "Allowed in guard tests".

ext_binary()
  a binary data object,
  structured according to the Erlang external term format

iodata = iolist() | binary()

iolist = [char() | binary() | iolist()]
  a binary is allowed as the tail of the list
    

Types:

Returns an integer or float which is the arithmetical absolute value of Number.

> abs(-3.33).
3.33000
> abs(-3).
3
        

Allowed in guard tests.

Types:

Returns a new tuple which has one element more than Tuple1, and contains the elements in Tuple1 followed by Term as the last element. Semantically equivalent to list_to_tuple(tuple_to_list(Tuple ++ [Term]), but much faster.

> erlang:append_element({one, two}, three).
{one,two,three}
        

Types:

Call a fun, passing the elements in Args as arguments.

Note: If the number of elements in the arguments are known at compile-time, the call is better written as Fun(Arg1, Arg2, ... ArgN).

Earlier, Fun could also be given as {Module, Function}, equivalent to apply(Module, Function, Args). This usage is deprecated and will stop working in a future release of Erlang/OTP.

Types:

Returns the result of applying Function in Module to Args. The applied function must be exported from Module. The arity of the function is the length of Args.

> apply(lists, reverse, [[a, b, c]]).
[c,b,a]
        

apply can be used to evaluate BIFs by using the module name erlang.

> apply(erlang, atom_to_list, ['Erlang']).
"Erlang"
        

Note: If the number of arguments are known at compile-time, the call is better written as Module:Function(Arg1, Arg2, ..., ArgN).

Failure: error_handler:undefined_function/3 is called if the applied function is not exported. The error handler can be redefined (see process_flag/2). If the error_handler is undefined, or if the user has redefined the default error_handler so the replacement module is undefined, an error with the reason undef is generated.

Types:

Returns a string which corresponds to the text representation of Atom.

> atom_to_list('Erlang').
"Erlang"
        

Types:

Returns a list of integers which correspond to the bytes of Binary.

Types:

As binary_to_list/1, but returns a list of integers corresponding to the bytes from position Start to position Stop in Binary. Positions in the binary are numbered starting from 1.

Types:

Returns an Erlang term which is the result of decoding the binary object Binary, which must be encoded according to the Erlang external term format. See also term_to_binary/1.

Types:

This implementation-dependent function increments the reduction counter for the calling process. In the Beam emulator, the reduction counter is normally incremented by one for each function and BIF call, and a context switch is forced when the counter reaches 1000.

This BIF might be removed in a future version of the Beam machine without prior warning. It is unlikely to be implemented in other Erlang implementations.

Types:

Cancels a timer, where TimerRef was returned by either erlang:send_after/3 or erlang:start_timer/3. If the timer is there to be removed, the function returns the time in milliseconds left until the timer would have expired, otherwise false (which means that TimerRef was never a timer, that it has already been cancelled, or that it has already delivered its message).

See also erlang:send_after/3, erlang:start_timer/3, and erlang:read_timer/1.

Note: Cancelling a timer does not guarantee that the message has not already been delivered to the message queue.

Types:

Returns true if the process Pid is executing old code for Module. That is, if the current call of the process executes old code for this module, or if the process has references to old code for this module, or if the process contains funs that references old code for this module. Otherwise, it returns false.

> check_process_code(Pid, lists).
false
        

See also code(3).

Do not use; use list_to_binary/1 instead.

Types:

Returns the current date as {Year, Month, Day}.

The time zone and daylight saving time correction depend on the underlying OS.

> date().
{1995, 2, 19}
        

Types:

Makes the current code for Module become old code, and deletes all references for this module from the export table. Returns undefined if the module does not exist, otherwise true.

This BIF is intended for the code server (see code(3)) and should not be used elsewhere.

Failure: badarg if there is already an old version of Module.

Types:

If MonitorRef is a reference which the calling process obtained by calling erlang:monitor/2, this monitoring is turned off. If the monitoring is already turned off, nothing happens.

Failure: It is an error if MonitorRef refers to a monitoring started by another process. Not all such cases are cheap to check; if checking is cheap, the call fails with badarg (for example if MonitorRef is a remote reference).

Types:

Forces the disconnection of a node. This will appear to the node Node as if the local node has crashed. This BIF is mainly used in the Erlang network authentication protocols. Returns true if disconnection succeeds, otherwise false. If the local node is not alive, the function returns ignored.

Types:

Prints a text representation of Term on the standard output.

This BIF is intended for debugging only.

Types:

Returns the Nth element (numbering from 1) of Tuple.

> element(2, {a, b, c}).
b
        

Allowed in guard tests.

Types:

Returns the process dictionary and deletes it.

> put(key1, {1, 2, 3}),
  put(key2, [a, b, c]),
  erase().
[{key1,{1,2,3}},{key2,[a,b,c]}]
        

Types:

Returns the value Val associated with Key and deletes it from the process dictionary. Returns undefined if no value is associated with Key.

> put(key1, {merry, lambs, are, playing}),
  X = erase(key1),
  {X, erase(key1)}.
{{merry,lambs,are,playing},undefined}
        

Types:

Stops the execution of the calling process with the reason Reason, where Reason is any term. The actual exit reason will be {Reason, Where}, where Where is a list of the functions most recently called (the current function first). Since evaluating this function causes the process to terminate, it has no return value.

> catch erlang:error(foobar).
{'EXIT',{foobar,[{erl_eval,do_apply,5},
                 {erl_eval,expr,5},
                 {shell,exprs,6},
                 {shell,eval_loop,3}]}}
        

Types:

Stops the execution of the calling process with the reason Reason, where Reason is any term. The actual exit reason will be {Reason, Where}, where Where is a list of the functions most recently called (the current function first). Args is expected to be the list of arguments for the current function; in Beam it will be used to provide the actual arguments for the current function in the Where term. Since evaluating this function causes the process to terminate, it has no return value.

Types:

Stops the execution of the calling process with the exit reason Reason, where Reason is any term. Since evaluating this function causes the process to terminate, it has no return value.

> exit(foobar).
** exited: foobar **
> catch exit(foobar).
{'EXIT', foobar}
        

Types:

Sends an exit signal with exit reason Reason to the process Pid.

The following behavior apply if Reason is any term except normal or kill:

If Pid is not trapping exits, Pid itself will exit with exit reason Reason. If Pid is trapping exits, the exit signal is transformed into a message {'EXIT', From, Reason} and delivered to the message queue of Pid. From is the pid of the process which sent the exit signal. See also process_flag/2.

If Reason is the atom normal, Pid will not exit. If it is trapping exits, the exit signal is transformed into a message {'EXIT', From, normal} and delivered to its message queue.

If Reason is the atom kill, that is if exit(Pid, kill) is called, an untrappable exit signal is sent to Pid which will unconditionally exit with exit reason killed.

Types:

Stops the execution of the calling process with the reason Reason. This an old equivalent to erlang:error(Reason).

Types:

Stops the execution of the calling process with the reason Reason. This an old equivalent to erlang:error(Reason, Args) .

Types:

Returns a float by converting Number to a float.

> float(55).
55.0000
        

Allowed in guard tests.

Note that if used on the top-level in a guard, it will test whether the argument is a floating point number; for clarity, use is_float/1 instead. When float/1 is used in an expression in a guard, such as 'float(A) == 4.0', it converts a number as described above.

Types:

Returns a string which corresponds to the text representation of Float.

> float_to_list(7.0).
"7.00000000000000000000e+00"
        

Types:

Returns a list containing information about the fun Fun. Each element of the list is a tuple. The order of the tuples is not defined, and more tuples may be added in a future release.

This BIF is mainly intended for debugging, but it can occasionally be useful in library functions that might need to verify, for instance, the arity of a fun.

There are two types of funs with slightly different semantics:

A fun created by fun M:F/A is called an external fun. Calling it will always call the function F with arity A in the latest code for module M. Note that module M does not even need to be loaded when the fun fun M:F/A is created.

All other funs are called local. When a local fun is called, the same version of the code that created the fun will be called (even if newer version of the module has been loaded).

The following elements will always be present in the list for both local and external funs:

{type, Type}

Type is either local or external.

{module, Module}

Module (an atom) is the module name.
If Fun is a local fun, Module is the module in which the fun is defined.
If Fun is an external fun, Module is the module that the fun refers to.

{name, Name}

Name (an atom) is a function name.
If Fun is a local fun, Name is the name of the local function that implements the fun. (This name was generated by the compiler, and is generally only of informational use. As it is a local function, it is not possible to call it directly.) If no code is currently loaded for the fun, [] will be returned instead of an atom.
If Fun is an external fun, Name is the name of the exported function that the fun refers to.

{arity, Arity}

Arity is the number of arguments that the fun should be called with.

{env, Env}

Env (a list) is the environment or free variables for the fun. (For external funs, the returned list is always empty.)

The following elements will only be present in the list if Fun is local:

{pid, Pid}

Pid is the pid of the process that originally created the fun.

{index, Index}

Index (an integer) is an index into the module's fun table.

{new_index, Index}

Index (an integer) is an index into the module's fun table.

{new_uniq, Uniq}

Uniq (a binary) is a unique value for this fun.

{uniq, Uniq}

Uniq (an integer) is a unique value for this fun.

Types:

Returns information about Fun as specified by Item, in the form {Item,Info}.

For any fun, Item can be any of the atoms module, name, arity, or env.

For a local fun, Item can also be any of the atoms index, new_index, new_uniq, uniq, and pid. For an external fun, the value of any of these items is always the atom undefined.

See erlang:fun_info/1.

Types:

Returns a string which corresponds to the text representation of Fun.

Types:

Returns true if the module Module is loaded and contains an exported function Function/Arity; otherwise false.

Returns false for any BIF (functions implemented in C rather than in Erlang).

This function is retained mainly for backwards compatibility.

Forces an immediate garbage collection of the currently executing process. The function should not be used, unless it has been noticed -- or there are good reasons to suspect -- that the spontaneous garbage collection will occur too late or not at all. Improper use may seriously degrade system performance.

Compatibility note: In versions of OTP prior to R7, the garbage collection took place at the next context switch, not immediately. To force a context switch after a call to erlang:garbage_collect(), it was sufficient to make any function call.

Types:

Works like erlang:garbage_collect() but on any process. The same caveats apply. Returns false if Pid refers to a dead process; true otherwise.

Types:

Returns the process dictionary as a list of {Key, Val} tuples.

> put(key1, merry),
  put(key2, lambs),
  put(key3, {are, playing}),
  get().
[{key1,merry},{key2,lambs},{key3,{are,playing}}]
        

Types:

Returns the value Valassociated with Key in the process dictionary, or undefined if Key does not exist.

> put(key1, merry),
  put(key2, lambs),
  put({any, [valid, term]}, {are, playing}),
  get({any, [valid, term]}).
{are,playing}
        

Types:

Returns the magic cookie of the local node, if the node is alive; otherwise the atom nocookie.

Types:

Returns a list of keys which are associated with the value Val in the process dictionary.

> put(mary, {1, 2}),
  put(had, {1, 2}),
  put(a, {1, 2}),
  put(little, {1, 2}),
  put(dog, {1, 3}),
  put(lamb, {1, 2}),
  get_keys({1, 2}).
[mary,had,a,little,lamb]
        

Types:

Get the stacktrace of the last exception in the calling process as a list of {Module,Function,Arity} tuples. The Arity field in the first tuple may be the argument list of that function call instead of an arity integer, depending on the exception.

If there has not been any exceptions in a process, the stacktrace is []. After a code change for the process, the stacktrace may also be reset to [].

The stacktrace is the same data as the catch operator returns, for example:

{'EXIT',{badarg,Stacktrace}} = catch abs(x)

See also erlang:error/1 and erlang:error/2.

Types:

Returns the pid of the group leader for the process which evaluates the function.

Every process is a member of some process group and all groups have a group leader. All IO from the group is channeled to the group leader. When a new process is spawned, it gets the same group leader as the spawning process. Initially, at system start-up, init is both its own group leader and the group leader of all processes.

Types:

Sets the group leader of Pid to GroupLeader. Typically, this is used when a processes started from a certain shell should have another group leader than init.

See also group_leader/0.

Halts the Erlang runtime system and indicates normal exit to the calling environment. Has no return value.

> halt().
os_prompt%
        

Types:

Status must be a non-negative integer, or a string. Halts the Erlang runtime system. Has no return value. If Status is an integer, it is returned as an exit status of Erlang to the calling environment. If Status is a string, produces an Erlang crash dump with String as slogan, and then exits with a non-zero status code.

Note that on many platforms, only the status codes 0-255 are supported by the operating system.

Returns a hash value for Term within the range 1..Range. The allowed range is 1..2^27-1.

This BIF is deprecated as the hash value may differ on different architectures. Also the hash values for integer terms larger than 2^27 as well as large binaries are very poor. The BIF is retained for backward compatibility reasons (it may have been used to hash records into a file), but all new code should use one of the BIFs erlang:phash/2 or erlang:phash2/1,2 instead.

Types:

Returns the head of List, that is, the first element.

> hd([1,2,3,4,5]).
1
        

Allowed in guard tests.

Failure: badarg if List is the empty list [].

Types:

Puts the calling process into a wait state where its memory allocation has been reduced as much as possible, which is useful if the process does not expect to receive any messages in the near future.

The process will be awaken when a message is sent to it, and control will resume in Module:Function with the arguments given by Args with the call stack emptied, meaning that the process will terminate when that function returns. Thus erlang:hibernate/3 will never return to its caller.

If the process has any message in its message queue, the process will be awaken immediately in the same way as described above.

In more technical terms, what erlang:hibernate/3 does is the following. It discards the call stack for the process. Then it garbage collects the process. After the garbage collection, all live data is in one continuous heap. The heap is then shrunken to the exact same size as the live data which it holds (even if that size is less than the minimum heap size for the process).

If the size of the live data in the process is less than the minimum heap size, the first garbage collection occurring after the process has been awaken will ensure that the heap size is changed to a size not smaller than the minimum heap size.

This BIF is now equivalent to erlang:system_info/1.

Types:

Returns a string which corresponds to the text representation of Integer.

> integer_to_list(77).
"77"
        

Types:

Returns a string which corresponds to the text representation of Integer in base Base.

> erlang:integer_to_list(1023, 16).
"3FF"
        

Types:

Returns a binary which is made from the integers and binaries in IoListOrBinary.

> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6>>.
<<6>>
> iolist_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6>>
        

Types:

Returns an integer which is the size in bytes of the binary that would be the result of iolist_to_binary(Item).

> iolist_size([1,2|<<3,4>>]).
4
        

Returns true if the local node is alive; that is, if the node can be part of a distributed system. Otherwise, it returns false.

Types:

Returns true if Term is an atom; otherwise returns false.

Allowed in guard tests.

Types:

Returns true if Term is a binary; otherwise returns false.

Allowed in guard tests.

Types:

Returns true if Term is either the atom true or the atom false (i.e. a boolean); otherwise returns false.

Allowed in guard tests.

Types:

Returns true if Module:Function/Arity is a BIF implemented in C; otherwise returns false. This BIF is useful for builders of cross reference tools.

Types:

Returns true if Term is a floating point number; otherwise returns false.

Allowed in guard tests.

Types:

Returns true if Term is a fun; otherwise returns false.

Allowed in guard tests.

Types:

Returns true if Term is a fun that can be applied with Arity number of arguments; otherwise returns false.

Allowed in guard tests.

Currently, is_function/2 will also return true if the first argument is a tuple fun (a tuple containing two atoms). In a future release, tuple funs will no longer be supported and is_function/2 will return false if given a tuple fun.

Types:

Returns true if Term is an integer; otherwise returns false.

Allowed in guard tests.

Types:

Returns true if Term is a list with zero or more elements; otherwise returns false.

Allowed in guard tests.

Types:

Returns true if Term is either an integer or a floating point number; otherwise returns false.

Allowed in guard tests.

Types:

Returns true if Term is a pid (process identifier); otherwise returns false.

Allowed in guard tests.

Types:

Returns true if Term is a port identifier; otherwise returns false.

Allowed in guard tests.

Types:

Pid must refer to a process at the local node. Returns true if the process exists and is alive, that is, has not exited. Otherwise, returns false.

Types:

Returns true if Term is a tuple and its first element is RecordTag. Otherwise, returns false.

Normally the compiler treats calls to is_record/2 specially. It emits code to verify that Term is a tuple, that its first element is RecordTag, and that the size is correct. However, if the RecordTag is not a literal atom, the is_record/3 BIF will be called instead.

Allowed in guard tests, if RecordTag is a literal atom.

Types:

RecordTag must be an atom. Returns true if Term is a tuple, its first element is RecordTag, and its size is Size. Otherwise, returns false.

This BIF is documented for completeness. In most cases is_record/2 should be used.

Types:

Returns true if Term is a reference; otherwise returns false.

Allowed in guard tests.

Types:

Returns true if Term is a tuple; otherwise returns false.

Allowed in guard tests.

Types:

Returns the length of List.

> length([1,2,3,4,5,6,7,8,9]).
9
        

Allowed in guard tests.

Types:

Creates a link between the calling process and another process (or port) Pid, if there is not such a link already. If a process attempts to create a link to itself, nothing is done. Returns true.

If Pid does not exist, the behavior of the BIF depends on if the calling process is trapping exits or not (see process_flag/2):

• If the calling process is not trapping exits, and checking Pid is cheap -- that is, if Pid is local -- link/1 fails with reason noproc.
• Otherwise, if the calling process is trapping exits, and/or Pid is remote, link/1 returns true, but an exit signal with reason noproc is sent to the calling process.

Types:

Returns the atom whose text representation is String.

> list_to_atom("Erlang").
'Erlang'
        

Types:

Returns a binary which is made from the integers and binaries in IoList.

> Bin1 = <<1,2,3>>.
<<1,2,3>>
> Bin2 = <<4,5>>.
<<4,5>>
> Bin3 = <<6>>.
<<6>>
> list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).
<<1,2,3,1,2,3,4,5,4,6>>
        

Types:

Returns the atom whose text representation is String, but only if there already exists such atom.

Failure: badarg if there does not already exist an atom whose text representation is String.

Types:

Returns the float whose text representation is String.

> list_to_float("2.2017764e+0").
2.20178
        

Failure: badarg if String contains a bad representation of a float.

Types:

Returns an integer whose text representation is String.

> list_to_integer("123").
123
        

Failure: badarg if String contains a bad representation of an integer.

Types:

Returns an integer whose text representation in base Base is String.

> erlang:list_to_integer("3FF", 16).
1023
        

Failure: badarg if String contains a bad representation of an integer.

Types:

Returns a pid whose text representation is String.

This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.

> list_to_pid("<0.4.1>").
<0.4.1>
        

Failure: badarg if String contains a bad representation of a pid.

Types:

Returns a tuple which corresponds to List. List can contain any Erlang terms.

> list_to_tuple([share, ['Ericsson_B', 163]]).
{share, ['Ericsson_B', 163]}
        

Types:

If Binary contains the object code for the module Module, this BIF loads that object code. Also, if the code for the module Module already exists, all export references are replaced so they point to the newly loaded code. The previously loaded code is kept in the system as old code, as there may still be processes which are executing that code. It returns either {module, Module}, or {error, Reason} if loading fails. Reason is one of the following:

badfile

The object code in Binary has an incorrect format.

not_purged

Binary contains a module which cannot be loaded because old code for this module already exists.

badfile

The object code contains code for another module than Module

This BIF is intended for the code server (see code(3)) and should not be used elsewhere.

Types:

Returns a list of all loaded Erlang modules (current and/or old code), including preloaded modules.

See also code(3).

Types:

Returns the current local date and time {{Year, Month, Day}, {Hour, Minute, Second}}.

The time zone and daylight saving time correction depend on the underlying OS.

> erlang:localtime().
{{1996,11,6},{14,45,17}}
        

Types:

Converts local date and time to Universal Time Coordinated (UTC), if this is supported by the underlying OS. Otherwise, no conversion is done and {Date1, Time1} is returned.

> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).
{{1996,11,6},{13,45,17}}
        

Failure: badarg if Date1 or Time1 do not denote a valid date or time.

Types:

Converts local date and time to Universal Time Coordinated (UTC) just like erlang:localtime_to_universaltime/1, but the caller decides if daylight saving time is active or not.

If IsDst == true the {Date1, Time1} is during daylight saving time, if IsDst == false it is not, and if IsDst == undefined the underlying OS may guess, which is the same as calling erlang:localtime_to_universaltime({Date1, Time1}).

> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, true).
{{1996,11,6},{12,45,17}}
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, false).
{{1996,11,6},{13,45,17}}
> erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, undefined).
{{1996,11,6},{13,45,17}}
        

Failure: badarg if Date1 or Time1 do not denote a valid date or time.

Returns an almost unique reference.

The returned reference will reoccur after approximately 2^82 calls; therefore it is unique enough for practical purposes.

> make_ref().
#Ref<0.0.0.135>
        

Types:

Returns a new tuple of the given Arity, where all elements are InitialValue.

> erlang:make_tuple(4, []).
{[],[],[],[]}
        

Types:

Computes an MD5 message digest from Data, where the length of the digest is 128 bits (16 bytes). Data is a binary or a list of small integers and binaries.

See The MD5 Message Digest Algorithm (RFC 1321) for more information about MD5.

Types:

Finishes the update of an MD5 Context and returns the computed MD5 message digest.

Types:

Creates an MD5 context, to be used in subsequent calls to md5_update/2.

Types:

Updates an MD5 Context with Data, and returns a NewContext.

Types:

Returns a list containing information about memory dynamically allocated by the Erlang emulator. Each element of the list is a tuple {Type, Size}. The first element Typeis an atom describing memory type. The second element Sizeis memory size in bytes. A description of each memory type follows:

total

The total amount of memory currently allocated, which is the same as the sum of memory size for processes and system.

processes

The total amount of memory currently allocated by the Erlang processes.

processes_used

The total amount of memory currently used by the Erlang processes.
This memory is part of the memory presented as processes memory.

system

The total amount of memory currently allocated by the emulator that is not directly related to any Erlang process.
Memory presented as processes is not included in this memory.

atom

The total amount of memory currently allocated for atoms.
This memory is part of the memory presented as system memory.

atom_used

The total amount of memory currently used for atoms.
This memory is part of the memory presented as atom memory.

binary

The total amount of memory currently allocated for binaries.
This memory is part of the memory presented as system memory.

code

The total amount of memory currently allocated for Erlang code.
This memory is part of the memory presented as system memory.

ets

The total amount of memory currently allocated for ets tables.
This memory is part of the memory presented as system memory.

maximum

The maximum total amount of memory allocated since the emulator was started.
This tuple is only present when the emulator is run with instrumentation.
For information on how to run the emulator with instrumentation see instrument(3) and/or erl(1).

The system value is not complete. Some allocated memory that should be part of the system value are not. For example, memory allocated by drivers is missing. When the emulator is run with instrumentation, the system value is more accurate, but memory directly allocated by malloc (and friends) are still not part of the system value. Direct calls to malloc are only done from OS specific runtime libraries and perhaps from user implemented Erlang drivers that do not use the memory allocation functions in the driver interface. Since the total value is the sum of processes and system the error in system will propagate to the total value.

The different values has the following relation to each other. Values beginning with an uppercase letter is not part of the result.

        total = processes + system
        processes = processes_used + ProcessesNotUsed
        system = atom + binary + code + ets + OtherSystem
        atom = atom_used + AtomNotUsed

        RealTotal = processes + RealSystem
        RealSystem = system + MissedSystem
        

The total value is supposed to be the total amount of memory dynamically allocated by the emulator. Shared libraries, the code of the emulator itself, and the emulator stack(s) are not supposed to be included. That is, the total value is not supposed to be equal to the total size of all pages mapped to the emulator. Furthermore, due to fragmentation and pre-reservation of memory areas, the size of the memory segments which contain the dynamically allocated memory blocks can be substantially larger than the total size of the dynamically allocated memory blocks.

More tuples in the returned list may be added in the future.

Types:

Returns the memory size in bytes allocated for memory of type Type. The argument can also be given as a list of Type atoms, in which case a corresponding list of {Type, Size} tuples is returned.

See erlang:memory/0.

Failure: badarg if the emulator is not run with instrumentation when Type == maximum.

Types:

Returns true if the module Module is loaded, otherwise returns false. It does not attempt to load the module.

This BIF is intended for the code server (see code(3)) and should not be used elsewhere.

Types:

The calling process starts monitoring Item which is an object of type Type.

Currently only processes can be monitored, i.e. the only allowed Type is process, but other types may be allowed in the future.

Item can be:

pid()

The pid of the process to monitor.

{RegName, Node}

A tuple consisting of a registered name of a process and a node name. The process residing on the node Node with the registered name RegName will be monitored.

RegName

The process locally registered as RegName will be monitored.

When a process is monitored by registered name, the process that has the registered name at the time when erlang:monitor/2 is called will be monitored. The monitor will not be effected, if the registered name is unregistered.

A 'DOWN' message will be sent to the monitoring process if Item dies, if Item does not exist, or if the connection is lost to the node which Item resides on. A 'DOWN' message has the following pattern:

{'DOWN', MonitorRef, Type, Object, Info}
        

where MonitorRef and Type are the same as described above, and:

Object

A reference to the monitored object:

• the pid of the monitored process, if Item was specified as a pid.
• {RegName, Node}, if Item was specifed as {RegName, Node}.
• {RegName, Node}, if Item was specified as RegName. Node will in this case be the name of the local node (node()).

Info

Either the exit reason of the process, noproc (non-existing process), or noconnection (no connection to Node).

If/when erlang:monitor/2 is extended (e.g. to handle other item types than process), other possible values for Object, and Info in the 'DOWN' message will be introduced.

The monitoring is turned off either when the 'DOWN' message is sent, or when erlang:demonitor/1 is called.

If an attempt is made to monitor a process on an older node (where remote process monitoring is not implemented or one where remote process monitoring by registered name is not implemented), the call fails with badarg.

Making several calls to erlang:monitor/2 for the same Item is not an error; it results in as many, completely independent, monitorings.

The format of the 'DOWN' message changed in the 5.2 version of the emulator (OTP release R9B) for monitor by registered name. The Object element of the 'DOWN' message could in earlier versions sometimes be the pid of the monitored process and sometimes be the registered name. Now the Object element is always a tuple consisting of the registered name and the node name. Processes on new nodes (emulator version 5.2 or greater) will always get 'DOWN' messages on the new format even if they are monitoring processes on old nodes. Processes on old nodes will always get 'DOWN' messages on the old format.

Types:

Monitors the status of the node Node. If Flag is true, monitoring is turned on; if Flag is false, monitoring is turned off.

Making several calls to monitor_node(Node, true) for the same Node is not an error; it results in as many, completely independent, monitorings.

If Node fails or does not exist, the message {nodedown, Node} is delivered to the process. If a process has made two calls to monitor_node(Node, true) and Node terminates, two nodedown messages are delivered to the process. If there is no connection to Node, there will be an attempt to create one. If this fails, a nodedown message is delivered.

Nodes connected through hidden connections can be monitored as any other node.

Failure: badargif the local node is not alive.

Types:

Returns the name of the local node. If the node is not alive, nonode@nohost is returned instead.

Allowed in guard tests.

Types:

Returns the node where Arg is located. Arg can be a pid, a reference, or a port. If the local node is not alive, nonode@nohost is returned.

Allowed in guard tests.

Types:

Returns a list of all visible nodes in the system, excluding the local node. Same as nodes(visible).

Types:

Returns a list of nodes according to argument given. The result returned when the argument is a list, is the list of nodes satisfying the disjunction(s) of the list elements.

Arg can be any of the following:

visible

Nodes connected to this node through normal connections.

hidden

Nodes connected to this node through hidden connections.

connected

All nodes connected to this node.

this

This node.

known

Nodes which are known to this node, i.e., connected, previously connected, etc.

Some equalities: [node()] = nodes(this), nodes(connected) = nodes([visible, hidden]), and nodes() = nodes(visible).

If the local node is not alive, nodes(this) == nodes(known) == [nonode@nohost], for any other Arg the empty list [] is returned.

Types:

Returns the tuple {MegaSecs, Secs, MicroSecs} which is the elapsed time since 00:00 GMT, January 1, 1970 (zero hour) on the assumption that the underlying OS supports this. Otherwise, some other point in time is chosen. It is also guaranteed that subsequent calls to this BIF returns continuously increasing values. Hence, the return value from now() can be used to generate unique time-stamps. It can only be used to check the local time of day if the time-zone info of the underlying operating system is properly configured.

Types:

Returns a port identifier as the result of opening a new Erlang port. A port can be seen as an external Erlang process. PortName is one of the following:

{spawn, Command}

Starts an external program. Command is the name of the external program which will be run. Command runs outside the Erlang work space unless an Erlang driver with the name Command is found. If found, that driver will be started. A driver runs in the Erlang workspace, which means that it is linked with the Erlang runtime system.
When starting external programs on Solaris, the system call vfork is used in preference to fork for performance reasons, although it has a history of being less robust. If there are problems with using vfork, setting the environment variable ERL_NO_VFORK to any value will cause fork to be used instead.

{fd, In, Out}

Allows an Erlang process to access any currently opened file descriptors used by Erlang. The file descriptor In can be used for standard input, and the file descriptor Out for standard output. It is only used for various servers in the Erlang operating system (shell and user). Hence, its use is very limited.

PortSettings is a list of settings for the port. Valid settings are:

{packet, N}

Messages are preceded by their length, sent in N bytes, with the most significant byte first. Valid values for N are 1, 2, or 4.

stream

Output messages are sent without packet lengths. A user-defined protocol must be used between the Erlang process and the external object.

{line, L}

Messages are delivered on a per line basis. Each line (delimited by the OS-dependent newline sequence) is delivered in one single message. The message data format is {Flag, Line}, where Flag is either eol or noeol and Line is the actual data delivered (without the newline sequence).
L specifies the maximum line length in bytes. Lines longer than this will be delivered in more than one message, with the Flag set to noeol for all but the last message. If end of file is encountered anywhere else than immediately following a newline sequence, the last line will also be delivered with the Flag set to noeol. In all other cases, lines are delivered with Flag set to eol.
The {packet, N} and {line, L} settings are mutually exclusive.

{cd, Dir}

This is only valid for {spawn, Command}. The external program starts using Dir as its working directory. Dir must be a string. Not available on VxWorks.

{env, Env}

This is only valid for {spawn, Command}. The environment of the started process is extended using the environment specifications in Env.
Env should be a list of tuples {Name, Val}, where Name is the name of an environment variable, and Val is the value it is to have in the spawned port process. Both Name and Val must be strings. The one exception is Val being the atom false (in analogy with os:getenv/1), which removes the environment variable. Not available on VxWorks.

exit_status

This is only valid for {spawn, Command} where Command refers to an external program.
When the external process connected to the port exits, a message of the form {Port,{exit_status,Status}} is sent to the connected process, where Status is the exit status of the external process. If the program aborts, on Unix the same convention is used as the shells do (i.e., 128+signal).
If the eof option has been given as well, the eof message and the exit_status message appear in an unspecified order.
If the port program closes its stdout without exiting, the exit_status option will not work.

use_stdio

This is only valid for {spawn, Command}. It allows the standard input and output (file descriptors 0 and 1) of the spawned (UNIX) process for communication with Erlang.

nouse_stdio

The opposite of use_stdio. Uses file descriptors 3 and 4 for communication with Erlang.

stderr_to_stdout

Affects ports to external programs. The executed program gets its standard error file redirected to its standard output file. stderr_to_stdout and nouse_stdio are mutually exclusive.

in

The port can only be used for input.

out

The port can only be used for output.

binary

All IO from the port are binary data objects as opposed to lists of bytes.

eof

The port will not be closed at the end of the file and produce an exit signal. Instead, it will remain open and a {Port, eof} message will be sent to the process holding the port.

The default is stream for all types of port and use_stdio for spawned ports.

Failure: If the port cannot be opened, the exit reason is the Posix error code which most closely describes the error, or einval if no Posix code is appropriate. The following Posix error codes may appear:

enomem

There was not enough memory to create the port.

eagain

There are no more available operating system processes.

enametoolong

The external command given was too long.

emfile

There are no more available file descriptors.

enfile

A file or port table is full.

During use of a port opened using {spawn, Name}, errors arising when sending messages to it are reported to the owning process using signals of the form {'EXIT', Port, PosixCode}. See file(3) for possible values of PosixCode.

The maximum number of ports that can be open at the same time is 1024 by default, but can be configured by the environment variable ERL_MAX_PORTS.

Types:

Portable hash function that will give the same hash for the same Erlang term regardless of machine architecture and ERTS version (the BIF was introduced in ERTS 4.9.1.1). Range can be between 1 and 2^32, the function returns a hash value for Term within the range 1..Range.

This BIF could be used instead of the old deprecated erlang:hash/2 BIF, as it calculates better hashes for all datatypes, but consider using phash2/1,2 instead.

Types:

Portable hash function that will give the same hash for the same Erlang term regardless of machine architecture and ERTS version (the BIF was introduced in ERTS 5.2). Range can be between 1 and 2^32, the function returns a hash value for Term within the range 0..Range-1. When called without the Range argument, a value in the range 0..2^27-1 is returned.

This BIF should always be used for hashing terms. It distributes small integers better than phash/2, and it is faster for bignums and binaries.

Note that the range 0..Range-1 is different from the range of phash/2 (1..Range).

Types:

Returns a string which corresponds to the text representation of Pid.

This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.

Types:

Closes an open port. Roughly the same as Port ! {self(), close} except for the error behaviour (see below), and that the port does not reply with {Port, closed}. Any process may close a port with port_close/1, not only the port owner (the connected process).

For comparison: Port ! {self(), close} fails with badarg if Port cannot be sent to (i.e., Port refers neither to a port nor to a process). If Port is a closed port nothing happens. If Port is an open port and the calling process is the port owner, the port replies with {Port, closed} when all buffers have been flushed and the port really closes, but if the calling process is not the port owner the port owner fails with badsig.

Note that any process can close a port using Port ! {PortOwner, close} just as if it itself was the port owner, but the reply always goes to the port owner.

In short: port_close(Port) has a cleaner and more logical behaviour than Port ! {self(), close}.

Failure: badarg if Port is not an open port or the registered name of an open port.

Types:

Sends data to a port. Same as Port ! {self(), {command, Data}} except for the error behaviour (see below). Any process may send data to a port with port_command/2, not only the port owner (the connected process).

For comparison: Port ! {self(), {command, Data}} fails with badarg if Port cannot be sent to (i.e., Port refers neither to a port nor to a process). If Port is a closed port the data message disappears without a sound. If Port is open and the calling process is not the port owner, the port owner fails with badsig. The port owner fails with badsig also if Data is not a valid IO list.

Note that any process can send to a port using Port ! {PortOwner, {command, Data}} just as if it itself was the port owner.

In short: port_command(Port, Data) has a cleaner and more logical behaviour than Port ! {self(), {command, Data}}.

Failure: badarg if Port is not an open port or the registered name of an open port.

Types:

Sets the port owner (the connected port) to Pid. Roughly the same as Port ! {self(), {connect, Pid}} except for the following:

• The error behavior differs, see below.
  
• The port does not reply with {Port,connected}.
  
• The new port owner gets linked to the port.
  

The old port owner stays linked to the port and have to call unlink(Port) if this is not desired. Any process may set the port owner to be any process with port_connect/2.

For comparison: Port ! {self(), {connect, Pid}} fails with badarg if Port cannot be sent to (i.e., Port refers neither to a port nor to a process). If Port is a closed port nothing happens. If Port is an open port and the calling process is the port owner, the port replies with {Port, connected} to the old port owner. Note that the old port owner is still linked to the port, and that the new is not. If Port is an open port and the calling process is not the port owner, the port owner fails with badsig. The port owner fails with badsig also if Pid is not an existing local pid.

Note that any process can set the port owner using Port ! {PortOwner, {connect, Pid}} just as if it itself was the port owner, but the reply always goes to the port owner.

In short: port_connect(Port, Pid) has a cleaner and more logical behaviour than Port ! {self(),{connect,Pid}}.

Failure: badarg if Port is not an open port or the registered name of an open port, or if Pid is not an existing local pid.

Types:

Performs a synchronous control operation on a port. The meaning of Operation and Data depends on the port, i.e., on the port driver. Not all port drivers support this control feature.

Returns: a list of integers in the range 0 through 255, or a binary, depending on the port driver. The meaning of the returned data also depends on the port driver.

Failure: badarg if Port is not an open port or the registered name of an open port, if Operation cannot fit in a 32-bit integer, if the port driver does not support synchronous control operations, or if the port driver so decides for any reason (probably something wrong with Operation or Data).

Types:

Performs a synchronous call to a port. The meaning of Operation and Data depends on the port, i.e., on the port driver. Not all port drivers support this feature.

Port is a port identifier, referring to a driver.

Operation is an integer, which is passed on to the driver.

Data is any Erlang term. This data is converted to binary term format and sent to the port.

Returns: a term from the driver. The meaning of the returned data also depends on the port driver.

Failure: badarg if Port is not an open port or the registered name of an open port, if Operation cannot fit in a 32-bit integer, if the port driver does not support synchronous control operations, or if the port driver so decides for any reason (probably something wrong with Operation or Data).

Types:

Returns a list containing tuples with information about the Port, or undefined if the port is not open. The order of the tuples is not defined, nor are all the tuples mandatory.

{registered_name, RegName}

RegName (an atom) is the registered name of the port. If the port has no registered name, this tuple is not present in the list.

{id, Index}

Index (an integer) is the internal index of the port. This index may be used to separate ports.

{connected, Pid}

Pid is the process connected to the port.

{links, Pids}

Pids is a list of pids to which processes the port is linked.

{name, String}

String is the command name set by open_port.

{input, Bytes}

Bytes is the total number of bytes read from the port.

{output, Bytes}

Bytes is the total number of bytes written to the port.

Failure: badarg if Port is not a local port.

Types:

Returns information about Port as specified by Item, or undefined if the port is not open. Also, if Item == registered_name and the port has no registered name, [] is returned.

For valid values of Item, and corresponding values of Info, see erlang:port_info/1.

Failure: badarg if Port is not a local port.

Types:

Returns a string which corresponds to the text representation of the port identifier Port.

This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.

Returns a list of all ports on the local node.

Types:

Returns a list of Erlang modules which are pre-loaded in the system. As all loading of code is done through the file system, the file system must have been loaded previously. Hence, at least the module init must be pre-loaded.

Types:

Writes information about the local process Pid on standard error. The currently allowed value for the atom Type is backtrace, which shows the contents of the stack, including information about the call chain, with the most recent data printed last. The format of the output is not further defined.

Types:

Sets certain flags for the process which calls this function. Returns the old value of the flag.

process_flag(trap_exit, Boolean)

When trap_exit is set to true, exit signals arriving to a process are converted to {'EXIT', From, Reason} messages, which can be received as ordinary messages. If trap_exit is set to false, the process exits if it receives an exit signal other than normal and the exit signal is propagated to its linked processes. Application processes should normally not trap exits.
See also exit/2.

process_flag(error_handler, Module)

This is used by a process to redefine the error handler for undefined function calls and undefined registered processes. Inexperienced users should not use this flag since code autoloading is dependent on the correct operation of the error handling module.

process_flag(min_heap_size, MinHeapSize)

This changes the minimum heap size for the calling process.

process_flag(priority, Level)

This sets the process priority. Level is an atom. All implementations support three priority levels, low, normal, and high. The default is normal.

process_flag(save_calls, N)

N must be an integer in the interval 0..10000. If N > 0, call saving is made active for the process, which means that information about the N most recent global function calls, BIF calls, sends and receives made by the process are saved in a list, which can be retrieved with process_info(Pid, last_calls). A global function call is one in which the module of the function is explicitly mentioned. Only a fixed amount of information is saved: a tuple {Module, Function, Arity} for function calls, and the mere atoms send, 'receive' and timeout for sends and receives ('receive' when a message is received and timeout when a receive times out). If N = 0, call saving is disabled for the process, which is the default. Whenever the size of the call saving list is set, its contents are reset.

Types:

Sets certain flags for the process Pid, in the same manner as process_flag/2. Returns the old value of the flag. The allowed values for Flag are only a subset of those allowed in process_flag/2, namely: save_calls.

Failure: badarg if Pid is not a local process.

Types:

Returns a list containing tuples with information about the process Pid, or undefined if the process is not alive. The order of the tuples is not defined, nor are all the tuples mandatory.

This BIF is intended for debugging only.

{current_function, {Module, Function, Args}}

Module, Function, Args is the current function call of the process.

{dictionary, Dictionary}

Dictionary is the dictionary of the process.

{error_handler, Module}

Module is the error handler module used by the process (for undefined function calls, for example).

{group_leader, GroupLeader}

GroupLeader is group leader for the IO of the process.

{heap_size, Size}

Size is the heap size of the process in heap words.

{initial_call, {Module, Function, Arity}}

Module, Function, Arity is the initial function call with which the process was spawned.

{links, Pids}

Pids is a list of pids, with processes to which the process has a link.

{message_queue_len, MessageQueueLen}

MessageQueueLen is the number of messages currently in the message queue of the process. This is the length of the list MessageQueue returned as the info item messages (see below).

{messages, MessageQueue}

MessageQueue is a list of the messages to the process, which have not yet been processed.

{priority, Level}

Level is the current priority level for the process. Only low and normal are always supported.

{reductions, Number}

Number is the number of reductions executed by the process.

{registered_name, Atom}

Atom is the registered name of the process. If the process has no registered name, this tuple is not present in the list.

{stack_size, Size}

Size is the stack size of the process in stack words.

{status, Status}

Status is the status of the process. Status is waiting (waiting for a message), running, runnable (ready to run, but another process is running), or suspended (suspended on a "busy" port or by the erlang:suspend_process/1 BIF).

{trap_exit, Boolean}

Boolean is true if the process is trapping exits, otherwise it is false.

Failure: badarg if Pid is not a local process.

Types:

Returns information about the process Pid as specified by Item, or undefined if the process is not alive. Also, if Item == registered_name and the process has no registered name, [] is returned.

The value of Item, and corresponding value of Info, can be any of the values specified for process_info/1.

In addition to the above, also the following items -- with corresponding values -- are allowed:

{backtrace, Bin}

The binary Bin contains the same information as the output from erlang:process_display(Pid, backtrace). Use binary_to_list/1 to obtain the string of characters from the binary.

{last_calls, false|Calls}

The value is false if call saving is not active for the process (see process_flag/3). If call saving is active, a list is returned, in which the last element is the most recent called.

{memory, Size}

Size is the size of the process in bytes. This includes stack, heap and internal structures.

{monitored_by, Pids}

A list of pids that are monitoring the process (with erlang:monitor/2).

{monitors, Monitors}

A list of monitors (started by erlang:monitor/2) that are active for the process. For a local process monitor or a remote process monitor by pid, the list item is {process, Pid}, and for a remote process monitor by name, the list item is {process, {RegName, Node}}.

Note however, that not all implementations support every one of the above Items.

Failure: badarg if Pid is not a local process.

Returns a list of all processes on the local node.

> processes().
[<0.0.0>,
 <0.2.0>,
 <0.4.0>,
 <0.5.0>,
 <0.7.0>,
 <0.8.0>]
        

Types:

Removes old code for Module. Before this BIF is used, erlang:check_process_code/2 should be called to check that no processes are executing old code in the module.

This BIF is intended for the code server (see code(3)) and should not be used elsewhere.

Failure: badarg if there is no old code for Module.

Types:

Adds a new Key to the process dictionary, associated with the value Val, and returns undefined. If Key already exists, the old value is deleted and replaced by Val and the function returns the old value.

The values stored when put is evaluated within the scope of a catch will not be retracted if a throw is evaluated, or if an error occurs.

> X = put(name, walrus), Y = put(name, carpenter),
  Z = get(name),
  {X, Y, Z}.
{undefined,walrus,carpenter}
        

Types:

Stops the execution of the calling process with an exception of given class, reason and stacktrace.

This BIF is intended for debugging and for use in the Erlang operating system. In general, it should be avoided in applications, unless you know very well what you are doing.

Class is one of error, exit or throw, so if it were not for the stacktrace erlang:raise(Class, Reason, Stacktrace) is equivalent to erlang:Class(Reason). Reason is any term and Stacktrace is a list as returned from get_stacktrace(), that is a list of 3-tuples {Module, Function, Arity | Args} where Module and Function are atoms and the third element is an integer arity or an argument list. The stacktrace may also contain {Fun, Args} tuples where Fun is a local fun and Args is an argument list.

The stacktrace is used as the exception stacktrace for the calling process; it will be truncated to the current maximum stacktrace depth.

Because evaluating this function causes the process to terminate, it has no return value - unless the arguments are invalid, in which case the function returns the error reason, that is badarg. If you want to be really sure not to return you can call erlang:error(erlang:raise(Class, Reason, Stacktrace)) and hope to distinguish exceptions later.

Types:

TimerRef is a timer reference returned by erlang:send_after/3 or erlang:start_timer/3. If the timer is active, the function returns the time in milliseconds left until the timer will expire, otherwise false (which means that TimerRef was never a timer, that it has been cancelled, or that it has already delivered its message).

See also erlang:send_after/3, erlang:start_timer/3, and erlang:cancel_timer/1.

Types:

Returns a string which corresponds to the text representation of Ref.

This BIF is intended for debugging and for use in the Erlang operating system. It should not be used in application programs.

Types:

Associates the name RegName with a pid or a port identifier. RegName, which must be an atom, can be used instead of the pid / port identifier in the send operator (RegName ! Message).

> register(db, Pid).
true
        

Failure: badarg if Pid is not an existing, local process or port, if RegName is already in use, if the process or port is already registered (already has a name), or if RegName is the atom undefined.

Types:

Returns a list of names which have been registered using register/2.

> registered().
[code_server, file_server, init, user, my_db]
        

Types:

Resume a suspended process Pid.

This BIF is intended for debugging only.

Failure: badarg if Pid does not exist.

Types:

Returns an integer by rounding Number.

> round(5.5).
6
        

Allowed in guard tests.

Returns the pid (process identifier) of the calling process.

> self().
<0.26.0>
        

Allowed in guard tests.

Types:

Sends a message and returns Msg. This is the same as Dest ! Msg.

Dest may be a remote or local pid, a (local) port, a locally registered name, or a tuple {RegName, Node} for a registered name at another node.

Types:

Sends a message and returns ok, or does not send the message but returns something else (see below). Otherwise the same as erlang:send/2. See also erlang:send_nosuspend/2,3. for more detailed explanation and warnings.

The possible options are:

nosuspend

If the sender would have to be suspended to do the send, nosuspend is returned instead.

noconnect

If the destination node would have to be autoconnected before doing the send, noconnect is returned instead.

As with erlang:send_nosuspend/2,3: Use with extreme care!

Types:

Starts a timer which will send the message Msg to Dest after Time milliseconds.

If Dest is an atom, it is supposed to be the name of a registered process. The process referred to by the name is looked up at the time of delivery. No error is given if the name does not refer to a process.

If Dest is a pid, the timer will be automatically canceled if the process referred to by the pid is not alive, or when the process exits. This feature was introduced in erts version 5.4.11. Note that timers will not be automatically canceled when Dest is an atom.

See also erlang:start_timer/3, erlang:cancel_timer/1, and erlang:read_timer/1.

Failure: badarg if the arguments does not satisfy the requirements specified above.

Types:

The same as erlang:send(Dest, Msg, [nosuspend]), but returns true if the message was sent and false if the message was not sent because the sender would have had to be suspended.

This function is intended for send operations towards an unreliable remote node without ever blocking the sending (Erlang) process. If the connection to the remote node (usually not a real Erlang node, but a node written in C or Java) is overloaded, this function will not send the message but return false instead.

The same happens, if Dest refers to a local port that is busy. For all other destinations (allowed for the ordinary send operator '!') this function sends the message and returns true.

This function