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.
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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
abs(Number) -> int() | float()
Types:
Number = number()
Returns an integer or float which is the arithmetical absolute value of Number.
> abs(-3.33). 3.33 > abs(-3). 3
Allowed in guard tests.
Types:
Data = iodata()
Computes and returns the adler32 checksum for Data.
adler32(OldAdler, Data) -> int()
Types:
OldAdler = int()
Data = iodata()
Continue computing the adler32 checksum by combining the previous checksum, OldAdler, with the checksum of Data.
The following code:
X = adler32(Data1),
Y = adler32(X,Data2).
- would assign the same value to Y as this would:
Y = adler32([Data1,Data2]).
adler32_combine(FirstAdler, SecondAdler, SecondSize) -> int()
Types:
FirstAdler = SecondAdler = int()
SecondSize = int()
Combines two previously computed adler32 checksums. This computation requires the size of the data object for the second checksum to be known.
The following code:
Y = adler32(Data1),
Z = adler32(Y,Data2).
- would assign the same value to Z as this would:
X = adler32(Data1),
Y = adler32(Data2),
Z = adler32_combine(X,Y,iolist_size(Data2)).
erlang:append_element(Tuple1, Term) -> Tuple2
Types:
Tuple1 = Tuple2 = tuple()
Term = term()
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}
apply(Fun, Args) -> term() | empty()
Types:
Fun = fun()
Args = [term()]
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.
apply(Module, Function, Args) -> term() | empty()
Types:
Module = Function = atom()
Args = [term()]
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.
atom_to_list(Atom) -> string()
Types:
Atom = atom()
Returns a string which corresponds to the text representation of Atom.
> atom_to_list('Erlang').
"Erlang"
binary_to_list(Binary) -> [char()]
Types:
Binary = binary()
Returns a list of integers which correspond to the bytes of Binary.
binary_to_list(Binary, Start, Stop) -> [char()]
Types:
Binary = binary()
Start = Stop = 1..byte_size(Binary)
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.
bitstring_to_list(Bitstring) -> [char()|bitstring()]
Types:
Bitstring = bitstring()
Returns a list of integers which correspond to the bytes of Bitstring. If the number of bits in the binary is not divisible by 8, the last element of the list will be a bitstring containing the remaining bits (1 up to 7 bits).
binary_to_term(Binary) -> term()
Types:
Binary = ext_binary()
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:
Bitstring = bitstring()
Returns an integer which is the size in bits of Bitstring.
> bit_size(<<433:16,3:3>>). 19 > bit_size(<<1,2,3>>). 24
Allowed in guard tests.
erlang:bump_reductions(Reductions) -> void()
Types:
Reductions = int()
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:
Bitstring = bitstring()
Returns an integer which is the number of bytes needed to contain Bitstring. (That is, if the number of bits in Bitstring is not divisible by 8, the resulting number of bytes will be rounded up.)
> byte_size(<<433:16,3:3>>). 3 > byte_size(<<1,2,3>>). 3
Allowed in guard tests.
erlang:cancel_timer(TimerRef) -> Time | false
Types:
TimerRef = ref()
Time = int()
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.
check_process_code(Pid, Module) -> bool()
Types:
Pid = pid()
Module = atom()
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:
Data = iodata()
Computes and returns the crc32 (IEEE 802.3 style) checksum for Data.
Types:
OldCrc = int()
Data = iodata()
Continue computing the crc32 checksum by combining the previous checksum, OldCrc, with the checksum of Data.
The following code:
X = crc32(Data1),
Y = crc32(X,Data2).
- would assign the same value to Y as this would:
Y = crc32([Data1,Data2]).
crc32_combine(FirstCrc, SecondCrc, SecondSize) -> int()
Types:
FirstCrc = SecondCrc = int()
SecondSize = int()
Combines two previously computed crc32 checksums. This computation requires the size of the data object for the second checksum to be known.
The following code:
Y = crc32(Data1),
Z = crc32(Y,Data2).
- would assign the same value to Z as this would:
X = crc32(Data1),
Y = crc32(Data2),
Z = crc32_combine(X,Y,iolist_size(Data2)).
Types:
Year = Month = Day = int()
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}
decode_packet(Type,Bin,Options) -> {ok,Packet,Rest} | {more,Length} | {error,Reason}
Types:
Bin = binary()
Options = [Opt]
Packet = binary() | HttpPacket
Rest = binary()
Length = int() | undefined
Reason = term()
Type, Opt -- see below
HttpPacket = HttpRequest | HttpResponse | HttpHeader | http_eoh | HttpError
HttpRequest = {http_request, HttpMethod, HttpUri, HttpVersion}
HttpResponse = {http_response, HttpVersion, integer(), string()}
HttpHeader = {http_header, int(), HttpField, Reserved=term(), Value=string()}
HttpError = {http_error, string()}
HttpMethod = HttpMethodAtom | string()
HttpMethodAtom = 'OPTIONS' | 'GET' | 'HEAD' | 'POST' | 'PUT' | 'DELETE' | 'TRACE'
HttpUri = '*' | {absoluteURI, http|https, Host=string(), Port=int()|undefined, Path=string()} |
{scheme, Scheme=string(), string()} | {abs_path, string} | string()
HttpVersion = {Major=int(), Minor=int()}
HttpField = HttpFieldAtom | string()
HttpFieldAtom = 'Cache-Control' | 'Connection' | 'Date' | 'Pragma' | 'Transfer-Encoding' | 'Upgrade' | 'Via' | 'Accept' | 'Accept-Charset' | 'Accept-Encoding' | 'Accept-Language' | 'Authorization' | 'From' | 'Host' | 'If-Modified-Since' | 'If-Match' | 'If-None-Match' | 'If-Range' | 'If-Unmodified-Since' | 'Max-Forwards' | 'Proxy-Authorization' | 'Range' | 'Referer' | 'User-Agent' | 'Age' | 'Location' | 'Proxy-Authenticate' | 'Public' | 'Retry-After' | 'Server' | 'Vary' | 'Warning' | 'Www-Authenticate' | 'Allow' | 'Content-Base' | 'Content-Encoding' | 'Content-Language' | 'Content-Length' | 'Content-Location' | 'Content-Md5' | 'Content-Range' | 'Content-Type' | 'Etag' | 'Expires' | 'Last-Modified' | 'Accept-Ranges' | 'Set-Cookie' | 'Set-Cookie2' | 'X-Forwarded-For' | 'Cookie' | 'Keep-Alive' | 'Proxy-Connection'
Decodes the binary Bin according to the packet protocol specified by Type. Very simular to the packet handling done by sockets with the option {packet,Type}.
If an entire packet is contained in Bin it is returned together with the remainder of the binary as {ok,Packet,Rest}.
If Bin does not contain the entire packet, {more,Length} is returned. Length is either the expected total size of the packet or undefined if the expected packet size is not known. decode_packet can then be called again with more data added.
If the packet does not conform to the protocol format {error,Reason} is returned.
The following values of Type are valid:
The following options are available:
> erlang:decode_packet(1,<<3,"abcd">>,[]).
{ok,<<"abc">>,<<"d">>}
> erlang:decode_packet(1,<<5,"abcd">>,[]).
{more,6}
delete_module(Module) -> true | undefined
Types:
Module = atom()
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.
erlang:demonitor(MonitorRef) -> true
Types:
MonitorRef = ref()
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.
Once erlang:demonitor(MonitorRef) has returned it is guaranteed that no {'DOWN', MonitorRef, _, _, _} message due to the monitor will be placed in the callers message queue in the future. A {'DOWN', MonitorRef, _, _, _} message might have been placed in the callers message queue prior to the call, though. Therefore, in most cases, it is advisable to remove such a 'DOWN' message from the message queue after monitoring has been stopped. erlang:demonitor(MonitorRef, [flush]) can be used instead of erlang:demonitor(MonitorRef) if this cleanup is wanted.
Prior to OTP release R11B (erts version 5.5) erlang:demonitor/1 behaved completely asynchronous, i.e., the monitor was active until the "demonitor signal" reached the monitored entity. This had one undesirable effect, though. You could never know when you were guaranteed not to receive a DOWN message due to the monitor.
Current behavior can be viewed as two combined operations: asynchronously send a "demonitor signal" to the monitored entity and ignore any future results of the monitor.
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).
erlang:demonitor(MonitorRef, OptionList) -> true
Types:
MonitorRef = ref()
OptionList = [Option]
Option = flush
erlang:demonitor(MonitorRef, []) is equivalent to erlang:demonitor(MonitorRef).
Currently the following Options are valid:
erlang:demonitor(MonitorRef),
receive
{_, MonitorRef, _, _, _} ->
true
after 0 ->
true
end
More options may be added in the future.
Failure: badarg if OptionList is not a list, or if Option is not a valid option, or the same failure as for erlang:demonitor/1
disconnect_node(Node) -> bool() | ignored
Types:
Node = atom()
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:
Term = term()
Prints a text representation of Term on the standard output.
This BIF is intended for debugging only.
Types:
N = 1..tuple_size(Tuple)
Tuple = tuple()
Returns the Nth element (numbering from 1) of Tuple.
> element(2, {a, b, c}).
b
Allowed in guard tests.
Types:
Key = Val = term()
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:
Key = Val = term()
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:
Reason = term()
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_exprs,6},
{shell,eval_loop,3}]}}
Types:
Reason = term()
Args = [term()]
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:
Reason = term()
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).
** exception exit: foobar
> catch exit(foobar).
{'EXIT',foobar}
Types:
Pid = pid()
Reason = term()
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:
Reason = term()
This function is deprecated and will be removed in the next release. Used erlang:error(Reason) instead.
Types:
Reason = term()
Args = [term()]
This function is deprecated and will be removed in the next release. Use erlang:error(Reason, Args) instead.
Types:
Number = number()
Returns a float by converting Number to a float.
> float(55). 55.0
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.
float_to_list(Float) -> string()
Types:
Float = float()
Returns a string which corresponds to the text representation of Float.
> float_to_list(7.0). "7.00000000000000000000e+00"
erlang:fun_info(Fun) -> [{Item, Info}]
Types:
Fun = fun()
Item, Info -- see below
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:
The following elements will only be present in the list if Fun is local:
erlang:fun_info(Fun, Item) -> {Item, Info}
Types:
Fun = fun()
Item, Info -- see below
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.
erlang:fun_to_list(Fun) -> string()
Types:
Fun = fun()
Returns a string which corresponds to the text representation of Fun.
erlang:function_exported(Module, Function, Arity) -> bool()
Types:
Module = Function = atom()
Arity = int()
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).
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.
garbage_collect(Pid) -> bool()
Types:
Pid = pid()
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:
Key = Val = term()
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:
Key = Val = term()
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}
erlang:get_cookie() -> Cookie | nocookie
Types:
Cookie = atom()
Returns the magic cookie of the local node, if the node is alive; otherwise the atom nocookie.
Types:
Val = Key = term()
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]
erlang:get_stacktrace() -> [{Module, Function, Arity | Args}]
Types:
Module = Function = atom()
Arity = int()
Args = [term()]
Get the call stack back-trace (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:
GroupLeader = pid()
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.
group_leader(GroupLeader, Pid) -> true
Types:
GroupLeader = Pid = pid()
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 = int()>=0 | string()
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.
erlang:hash(Term, Range) -> Hash
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:
List = [term()]
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 [].
erlang:hibernate(Module, Function, Args)
Types:
Module = Function = atom()
Args = [term()]
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.
Note that emptying the call stack means that any surrounding catch is removed and has to be re-inserted after hibernation. One effect of this is that processes started using proc_lib (also indirectly, such as gen_server processes), should use proc_lib:hibernate/3 instead to ensure that the exception handler continues to work when the process wakes up.
integer_to_list(Integer) -> string()
Types:
Integer = int()
Returns a string which corresponds to the text representation of Integer.
> integer_to_list(77). "77"
erlang:integer_to_list(Integer, Base) -> string()
Types:
Integer = int()
Base = 2..36
Returns a string which corresponds to the text representation of Integer in base Base.
> erlang:integer_to_list(1023, 16). "3FF"
iolist_to_binary(IoListOrBinary) -> binary()
Types:
IoListOrBinary = iolist() | binary()
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:
Item = iolist() | binary()
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:
Term = term()
Returns true if Term is an atom; otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a binary; otherwise returns false.
A binary always contains a complete number of bytes.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a bitstring (including a binary); otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is either the atom true or the atom false (i.e. a boolean); otherwise returns false.
Allowed in guard tests.
erlang:is_builtin(Module, Function, Arity) -> bool()
Types:
Module = Function = atom()
Arity = int()
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:
Term = term()
Returns true if Term is a floating point number; otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a fun; otherwise returns false.
Allowed in guard tests.
is_function(Term, Arity) -> bool()
Types:
Term = term()
Arity = int()
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:
Term = term()
Returns true if Term is an integer; otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a list with zero or more elements; otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is either an integer or a floating point number; otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a pid (process identifier); otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a port identifier; otherwise returns false.
Allowed in guard tests.
is_process_alive(Pid) -> bool()
Types:
Pid = pid()
Pid must refer to a process at the local node. Returns true if the process exists and is alive, that is, is not exiting and has not exited. Otherwise, returns false.
is_record(Term, RecordTag) -> bool()
Types:
Term = term()
RecordTag = atom()
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/2 BIF will be called instead and the size of the tuple will not be verified.
Allowed in guard tests, if RecordTag is a literal atom.
is_record(Term, RecordTag, Size) -> bool()
Types:
Term = term()
RecordTag = atom()
Size = int()
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.
Allowed in guard tests, provided that RecordTag is a literal atom and Size is a literal integer.
This BIF is documented for completeness. In most cases is_record/2 should be used.
Types:
Term = term()
Returns true if Term is a reference; otherwise returns false.
Allowed in guard tests.
Types:
Term = term()
Returns true if Term is a tuple; otherwise returns false.
Allowed in guard tests.
Types:
List = [term()]
Returns the length of List.
> length([1,2,3,4,5,6,7,8,9]). 9
Allowed in guard tests.
Types:
Pid = pid() | port()
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):
list_to_atom(String) -> atom()
Types:
String = string()
Returns the atom whose text representation is String.
> list_to_atom("Erlang").
'Erlang'
list_to_binary(IoList) -> binary()
Types:
IoList = iolist()
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>>
list_to_bitstring(BitstringList) -> bitstring()
Types:
BitstringList = [BitstringList | bitstring() | char()]
Returns a bitstring which is made from the integers and bitstrings in BitstringList. (The last tail in BitstringList is allowed to be a bitstring.)
> Bin1 = <<1,2,3>>. <<1,2,3>> > Bin2 = <<4,5>>. <<4,5>> > Bin3 = <<6,7:4,>>. <<6>> > list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]). <<1,2,3,1,2,3,4,5,4,6,7:46>>
list_to_existing_atom(String) -> atom()
Types:
String = string()
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.
list_to_float(String) -> float()
Types:
String = string()
Returns the float whose text representation is String.
> list_to_float("2.2017764e+0").
2.2017764
Failure: badarg if String contains a bad representation of a float.
list_to_integer(String) -> int()
Types:
String = string()
Returns an integer whose text representation is String.
> list_to_integer("123").
123
Failure: badarg if String contains a bad representation of an integer.
erlang:list_to_integer(String, Base) -> int()
Types:
String = string()
Base = 2..36
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:
String = string()
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.
list_to_tuple(List) -> tuple()
Types:
List = [term()]
Returns a tuple which corresponds to List. List can contain any Erlang terms.
> list_to_tuple([share, ['Ericsson_B', 163]]).
{share, ['Ericsson_B', 163]}
load_module(Module, Binary) -> {module, Module} | {error, Reason}
Types:
Module = atom()
Binary = binary()
Reason = badfile | not_purged | badfile
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:
This BIF is intended for the code server (see code(3)) and should not be used elsewhere.
Types:
Module = atom()
Returns a list of all loaded Erlang modules (current and/or old code), including preloaded modules.
See also code(3).
erlang:localtime() -> {Date, Time}
Types:
Date = {Year, Month, Day}
Time = {Hour, Minute, Second}
Year = Month = Day = Hour = Minute = Second = int()
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}}
erlang:localtime_to_universaltime({Date1, Time1}) -> {Date2, Time2}
Types:
Date1 = Date2 = {Year, Month, Day}
Time1 = Time2 = {Hour, Minute, Second}
Year = Month = Day = Hour = Minute = Second = int()
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.
erlang:localtime_to_universaltime({Date1, Time1}, IsDst) -> {Date2, Time2}
Types:
Date1 = Date2 = {Year, Month, Day}
Time1 = Time2 = {Hour, Minute, Second}
Year = Month = Day = Hour = Minute = Second = int()
IsDst = true | false | undefined
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 re-occur after approximately 2^82 calls; therefore it is unique enough for practical purposes.
> make_ref(). #Ref<0.0.0.135>
erlang:make_tuple(Arity, InitialValue) -> tuple()
Types:
Arity = int()
InitialValue = term()
Returns a new tuple of the given Arity, where all elements are InitialValue.
> erlang:make_tuple(4, []).
{[],[],[],[]}
Types:
Data = iodata()
Digest = binary()
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.
The MD5 Message Digest Algorithm is not considered safe for code-signing or software integrity purposes.
erlang:md5_final(Context) -> Digest
Types:
Context = Digest = binary()
Finishes the update of an MD5 Context and returns the computed MD5 message digest.
Types:
Context = binary()
Creates an MD5 context, to be used in subsequent calls to md5_update/2.
erlang:md5_update(Context, Data) -> NewContext
Types:
Data = iodata()
Context = NewContext = binary()
Updates an MD5 Context with Data, and returns a NewContext.
erlang:memory() -> [{Type, Size}]
Types:
Type, Size -- see below
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:
The system value is not complete. Some allocated memory that should be part of the system value are not.
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 amounts of memory that are summed are not gathered atomically which also introduce an error in the result.
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
More tuples in the returned list may be added in the future.
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.
Since erts version 5.6.4 erlang:memory/0 requires that all erts_alloc(3) allocators are enabled (default behaviour).
Failure:
erlang:memory(Type | [Type]) -> Size | [{Type, Size}]
Types:
Type, Size -- see below
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.
Since erts version 5.6.4 erlang:memory/1 requires that all erts_alloc(3) allocators are enabled (default behaviour).
Failures:
See also erlang:memory/0.
module_loaded(Module) -> bool()
Types:
Module = atom()
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.
erlang:monitor(Type, Item) -> MonitorRef
Types:
Type = process
Item = pid() | {RegName, Node} | RegName
RegName = atom()
Node = node()
MonitorRef = reference()
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:
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:
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.
monitor_node(Node, Flag) -> true
Types:
Node = node()
Flag = bool()
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.
erlang:monitor_node(Node, Flag, Options) -> true
Types:
Node = node()
Flag = bool()
Options = [Option]
Option = allow_passive_connect
Behaves as monitor_node/2 except that it allows an extra option to be given, namely allow_passive_connect. The option allows the BIF to wait the normal net connection timeout for the monitored node to connect itself, even if it cannot be actively connected from this node (i.e. it is blocked). The state where this might be useful can only be achieved by using the kernel option dist_auto_connect once. If that kernel option is not used, the allow_passive_connect option has no effect.
The allow_passive_connect option is used internally and is seldom needed in applications where the network topology and the kernel options in effect is known in advance.
Failure: badarg if the local node is not alive or the option list is malformed.
Types:
Node = node()
Returns the name of the local node. If the node is not alive, nonode@nohost is returned instead.
Allowed in guard tests.
Types:
Arg = pid() | port() | ref()
Node = node()
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:
Nodes = [node()]
Returns a list of all visible nodes in the system, excluding the local node. Same as nodes(visible).
Types:
Arg = visible | hidden | connected | this | known
Nodes = [node()]
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:
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.
now() -> {MegaSecs, Secs, MicroSecs}
Types:
MegaSecs = Secs = MicroSecs = int()
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.
open_port(PortName, PortSettings) -> port()
Types:
PortName = {spawn, Command} | {fd, In, Out}
Command = string()
In = Out = int()
PortSettings = [Opt]
Opt = {packet, N} | stream | {line, L} | {cd, Dir} | {env, Env} | exit_status | use_stdio | nouse_stdio | stderr_to_stdout | in | out | binary | eof
N = 1 | 2 | 4
L = int()
Dir = string()
Env = [{Name, Val}]
Name = string()
Val = string() | false
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:
PortSettings is a list of settings for the port. Valid settings are:
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 badarg, system_limit, or the Posix error code which most closely describes the error, or einval if no Posix code is appropriate:
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.
erlang:phash(Term, Range) -> Hash
Types:
Term = term()
Range = 1..2^32
Hash = 1..Range
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 data-types, but consider using phash2/1,2 instead.
erlang:phash2(Term [, Range]) -> Hash
Types:
Term = term()
Range = 1..2^32
Hash = 0..Range-1
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:
Pid = pid()
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:
Port = port() | atom()
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.
port_command(Port, Data) -> true
Types:
Port = port() | atom()
Data = iodata()
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.
port_connect(Port, Pid) -> true
Types:
Port = port() | atom()
Pid = pid()
Sets the port owner (the connected port) to Pid. Roughly the same as Port ! {self(), {connect, Pid}} except for the following:
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.
port_control(Port, Operation, Data) -> Res
Types:
Port = port() | atom()
Operation = int()
Data = Res = iodata()
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).
erlang:port_call(Port, Operation, Data) -> term()
Types:
Port = port() | atom()
Operation = int()
Data = term()
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).
erlang:port_info(Port) -> [{Item, Info}] | undefined
Types:
Port = port() | atom()
Item, Info -- see below
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.