binary(3)

NAME
binary - Library for handling binary data.

DESCRIPTION

This module provides functions for manipulating byte-oriented binaries. While most of these functions could be implemented using the bit syntax, the functions in this module are highly optimized and are expected to either execute faster or consume less memory, or both, compared to equivalent implementations written in pure Erlang.

The module is provided according to EEP 31: Binary manipulation and searching module.

NOTE: This module handles byte-oriented data. For bitstrings that are not binaries (does not contain whole octets of bits) a badarg exception is raised from any of the functions in this module.

DATA TYPES

-opaque cp()

    Opaque data type representing a compiled search pattern.

    Guaranteed to be a tuple/0 to allow programs to distinguish it from non-precompiled search patterns.
part() :: {Start :: non_neg_integer(), Length :: integer()}.

    A representation of a part (or range) in a binary. Start is a zero-based offset into a binary/0 and Length is the length of that part.

    As input to functions in this module, a reverse part specification is allowed, constructed with a negative Length, so that the part of the binary begins at Start + Length and is -Length long. This is useful for referencing the last N bytes of a binary as {size(Binary), -N}. The functions in this module always return part/0s with positive Length.

FUNCTIONS

at(Subject, Pos) -> byte() when Subject :: binary(), Pos :: non_neg_integer().

    Returns the byte at position Pos (zero-based) in binary Subject as an integer.

    If Pos >= byte_size(Subject), a badarg exception is raised.

  Examples

    1> binary:at(<<5,19,72,33>>, 0).
    5
    2> binary:at(<<5,19,72,33>>, 1).
    19
    3> binary:at(<<5,19,72,33>>, 4).
    ** exception error: bad argument
         in function  binary:at/2
            called as binary:at(<<5,19,72,33>>,4)
bin_to_list(Subject) -> [byte()] when Subject :: binary().

    Converts Subject to a list of byte()s, each representing the value of one byte.

  Examples

    1> binary:bin_to_list(<<"erlang",0>>).
    [101,114,108,97,110,103,0]
bin_to_list(Subject, Pos, Len) -> [byte()] when Subject :: binary(), Pos :: non_neg_integer(), Len :: integer().

    Converts part of Subject to a list of byte/0s, each representing the value of one byte.

    Pos and Len denote which part of the Subject binary to convert.

  Examples

    1> binary:bin_to_list(<<"erlang">>, 1, 3).
    "rla"
    %% or [114,108,97] in list notation.
    2> binary:bin_to_list(<<"erlang">>, 5, 3).
    ** exception error: bad argument
         in function  binary:bin_to_list/3
            called as binary:bin_to_list(<<"erlang">>,5,3)
            *** argument 3: out of range

If Pos and Len reference outside the binary in any way, a badarg exception is raised.
compile_pattern(Pattern) -> cp() when Pattern :: PatternBinary | [PatternBinary, ...], PatternBinary :: nonempty_binary().

    Builds an internal structure representing a compilation of a search pattern, later to be used in functions match/3, matches/3, split/3, or replace/4.

    The cp/0 returned is guaranteed to be a tuple/0 to allow programs to distinguish it from non-precompiled search patterns.

    When a list of binaries is specified, it denotes a set of alternative binaries to search for. For example, if [<<"functional">>,<<"programming">>] is specified as Pattern, this means either <<"functional">> or <<"programming">>". The pattern is a set of alternatives; when only a single binary is specified, the set has only one element. The order of alternatives in a pattern is not significant.

    The list of binaries used for search alternatives must be flat, proper, and non-empty.

    If Pattern is not a binary or a flat proper non-empty list of binaries with length greater than 0, a badarg exception is raised.

  Examples

    1> Pat = binary:compile_pattern(~"rain").
    2> binary:match(~"the rain in spain", Pat).
    {4,4}
copy(Subject) -> binary() when Subject :: binary().

    Creates a copy of Subject.

    Using copy/1 on a binary that references a larger binary can potentially free up the larger binary for garbage collection.

    NOTE: Deliberately copying a single binary to avoid referencing a larger binary does not necessarily free up the larger binary for garbage collection. Instead, it can lead to the creation of significantly more binary data than needed. In general, sharing binary data is beneficial. Only in special cases — when small parts reference large binaries and the large binaries are no longer used in any process — can deliberate copying be beneficial.

  Examples

    1> HugeBinary = <<0:100_000/unit:8>>.
    2> byte_size(HugeBinary).
    100000
    3> Part = binary:part(HugeBinary, 0, 5).
    <<0,0,0,0,0>>
    4> Copy = binary:copy(Part).
    <<0,0,0,0,0>>
copy(Subject, N) -> binary() when Subject :: binary(), N :: non_neg_integer().

    Creates a binary with the content of Subject duplicated N times.

    This function always creates a new binary, even when N is 1.

  Examples

    1> binary:copy(~"-", 10).
    <<"----------">>
decode_hex(Bin) -> Bin2 when Bin :: <<_:_*16>>, Bin2 :: binary().

    Decodes a hex-encoded binary into a binary.

    An exception is raised if the size of the binary is not evenly divisble by two, or if the binary contains any characters that do not represent hex digits.

  Examples

    1> binary:decode_hex(<<"666f6f">>).
    <<"foo">>
    2> binary:decode_hex(<<"A">>).
    ** exception error: bad argument
         in function  binary:decode_hex/1
            called as binary:decode_hex(<<"A">>)
            *** argument 1: must contain an even number of bytes
decode_unsigned(Subject, Endianness) -> Unsigned when Subject :: binary(), Endianness :: big | little, Unsigned :: non_neg_integer().

    Converts the binary digit representation, in big endian or little endian, of a positive integer in Subject to an Erlang integer/0.

  Examples

    1> binary:decode_unsigned(<<7>>).
    7
    2> binary:decode_unsigned(<<1,0>>).
    256
    3> binary:decode_unsigned(<<169,138,199>>).
    11111111
    4> binary:decode_unsigned(<<169,138,199>>, big).
    11111111
    5> binary:decode_unsigned(<<169,138,199>>, little).
    13077161
encode_hex(Bin, Case) -> Bin2 when Bin :: binary(), Case :: lowercase | uppercase, Bin2 :: <<_:_*16>>.

    Encodes a binary into a hex-encoded binary using the specified case for the hexadecimal digits "a" to "f".

  Examples

    1> binary:encode_hex(<<"foo">>, uppercase).
    <<"666F6F">>
    2> binary:encode_hex(<<"/">>, uppercase).
    <<"2F">>
    3> binary:encode_hex(<<"/">>, lowercase).
    <<"2f">>
encode_unsigned(Unsigned, Endianness) -> binary() when Unsigned :: non_neg_integer(), Endianness :: big | little.

    Converts a non-negative integer into the smallest possible unsigned binary representation, using either big-endian or little-endian format.

    If Unsigned is not a non-negative integer, a badarg exception is raised.

  Examples

    1> binary:encode_unsigned(0, big).
    <<0>>
    2> binary:encode_unsigned(255, big).
    <<255>>
    3> binary:encode_unsigned(256, big).
    <<1,0>>
    4> binary:encode_unsigned(256, little).
    <<0,1>>
    5> binary:encode_unsigned(11111111, big).
    <<169,138,199>>
    6> binary:encode_unsigned(11111111, little).
    <<199,138,169>>
first(Subject) -> byte() when Subject :: binary().

    Returns the first byte of binary Subject as an integer.

    If the size of Subject is zero, a badarg exception is raised.

  Examples

    1> binary:first(<<42,99,100>>).
    42
    2> binary:first(<<>>).
    ** exception error: bad argument
         in function  binary:first/1
            called as binary:first(<<>>)
            *** argument 1: a zero-sized binary is not allowed
join([binary()], binary()) -> binary().

    Joins a list of binaries together by a specified Separator.

    Equivalent to iolist_to_binary(lists:join(Separator, Binaries)), but faster.

  Examples

    1> binary:join([<<"a">>, <<"b">>, <<"c">>], <<", ">>).
    <<"a, b, c">>
last(Subject) -> byte() when Subject :: binary().

    Returns the last byte of binary Subject as an integer.

    If the size of Subject is zero, a badarg exception is raised.

  Examples

    1> binary:last(<<42,99,100>>).
    100
    2> binary:last(<<>>).
    ** exception error: bad argument
         in function  binary:last/1
            called as binary:last(<<>>)
            *** argument 1: a zero-sized binary is not allowed
list_to_bin(ByteList) -> binary() when ByteList :: iolist().

    Works exactly as erlang:list_to_binary/1.

    This function is provided for completeness.
longest_common_prefix(Binaries) -> non_neg_integer() when Binaries :: [binary(), ...].

    Returns the length of the longest common prefix of the binaries in list Binaries.

    If Binaries is not a flat non-empty list of binaries, a badarg exception is raised.

  Examples

    1> binary:longest_common_prefix([<<"erlang">>, <<"ergonomy">>]).
    2
    2> binary:longest_common_prefix([<<"erlang">>, <<"perl">>]).
    0
longest_common_suffix(Binaries) -> non_neg_integer() when Binaries :: [binary(), ...].

    Returns the length of the longest common suffix of the binaries in list Binaries.

    If Binaries is not a flat non-empty list of binaries, a badarg exception is raised.

  Examples

    1> binary:longest_common_suffix([<<"erlang">>, <<"fang">>]).
    3
    2> binary:longest_common_suffix([<<"erlang">>, <<"perl">>]).
    0
match(Subject, Pattern, Options) -> Found | nomatch when Subject :: binary(), Pattern :: PatternBinary | [PatternBinary, ...] | cp(), PatternBinary :: nonempty_binary(), Found :: part(), Options :: [Option], Option :: {scope, part()}.

    Searches for the first occurrence of Pattern in Subject and returns the position and length.

    The function returns {Pos, Length} for the binary in Pattern, starting at the lowest position in Subject.

    Summary of the options: {scope, {Start, Length}}
        Only the specified part is searched. Return values still have offsets from the beginning of Subject. A negative Length is allowed as described in Types.

    If none of the strings in Pattern is found, the atom nomatch is returned.

    For a description of Pattern, see compile_pattern/1.

    If {scope, {Start,Length}} is specified in the options such that Start > size of Subject, Start + Length < 0 or Start + Length > size of Subject, a badarg exception is raised.

  Examples

    1> binary:match(<<"abcde">>, [<<"bcde">>, <<"cd">>], []).
    {1,4}

Even though <<"cd">> ends before <<"bcde">>, <<"bcde">> begins first and is therefore the first match. If two overlapping matches begin at the same position, the longest is returned.

    1> binary:match(~"the rain in spain", ~"ain", []).
    {5,3}
matches(Subject, Pattern, Options) -> Found when Subject :: binary(), Pattern :: PatternBinary | [PatternBinary, ...] | cp(), PatternBinary :: nonempty_binary(), Found :: [part()], Options :: [Option], Option :: {scope, part()}.

    As match/2, but Subject is searched until exhausted and a list of all non-overlapping parts matching Pattern is returned (in order).

    The first and longest match is preferred to a shorter, which is illustrated by the following example:

        1> binary:matches(<<"abcde">>,
                          [<<"bcde">>,<<"bc">>,<<"de">>],
                          []).
        [{1,4}]

    The result shows that <<"bcde">> is selected instead of the shorter match <<"bc">> (which would have resulted in one more match, <<"de">>). This corresponds to the behavior of POSIX regular expressions (and programs such as awk), but is not consistent with alternative matches in re (and Perl), where lexical ordering in the search pattern determines which string matches.

    If none of the strings in a pattern is found, an empty list is returned.

    For a description of Pattern, see compile_pattern/1. For a description of available options, see match/3.

    If {scope, {Start,Length}} is specified in the options such that Start > size of Subject, Start + Length < 0 or Start + Length is > size of Subject, a badarg exception is raised.

  Examples

    1> binary:matches(~"the rain in spain", ~"ai", []).
    [{5,2},{14,2}]
part(Subject, Pos, Len) -> binary() when Subject :: binary(), Pos :: non_neg_integer(), Len :: integer().

    Extracts the part of binary Subject described by PosLen.

    A negative length can be used to extract bytes at the end of a binary.

    NOTE: part/2 and part/3 are also available in the erlang module under the names binary_part/2 and binary_part/3. Those BIFs are allowed in guard tests.

    If Pos and Len in any way references outside the binary, a badarg exception is raised.

  Examples

    1> Bin = <<1,2,3,4,5,6,7,8,9,10>>.
    2> binary:part(Bin, 1, 3).
    <<2,3,4>>
    3> binary:part(Bin, byte_size(Bin), -5).
    <<6,7,8,9,10>>
referenced_byte_size(Binary) -> non_neg_integer() when Binary :: binary().

    Get the size of the underlying binary referenced by Binary.

    If a binary references a larger binary (often called a subbinary), it can be useful to determine the size of the referenced binary. This function can be used to decide when to trigger copy/1. Copying a binary can help eliminate the reference to the original, potentially large, binary that the smaller binary depends on.

    NOTE: Binary data is shared among processes. If another process still references the larger binary, copying only the part used by this process will consume more memory without freeing the larger binary for garbage collection. Use these intrusive functions with extreme care, and only when a real problem has been identified.

  Examples

    store(Binary, GBSet) ->
        NewBin =
            case binary:referenced_byte_size(Binary) of
                Large when Large > 2 * byte_size(Binary) ->
                    binary:copy(Binary);
                _ ->
                    Binary
            end,
        gb_sets:insert(NewBin, GBSet).

In this example, we choose to copy the binary content before inserting it into gb_sets:set() if it references a binary more than twice the size of the data we want to retain. Naturally, different rules apply when copying in different applications.

Binary sharing occurs whenever binaries are taken apart. This is the fundamental reason why binaries are efficient; decomposition always has O(1) complexity. However, in rare circumstances this data sharing is undesirable. In such situations, this function, along with copy/1 can be useful for optimizing memory usage.

    1> A = binary:copy(<<1>>, 1000).
    <<1,1,1,1,1,_/binary>>
    2> byte_size(A).
    1000
    3> binary:referenced_byte_size(A).
    1000
    4> <<B:10/binary, C/binary>> = A.
    5> {byte_size(B), binary:referenced_byte_size(B)}.
    {10,10}
    6> {byte_size(C), binary:referenced_byte_size(C)}.
    {990,1000}

In the above example, the small binary B was copied, while the larger binary C still references binary A.
replace(Subject, Pattern, Replacement, Options) -> Result when Subject :: binary(), Pattern :: PatternBinary | [PatternBinary, ...] | cp(), PatternBinary :: nonempty_binary(), Replacement :: binary() | fun((binary()) -> binary()), Options :: [Option], Option :: global | {scope, part()} | {insert_replaced, InsPos}, InsPos :: OnePos | [OnePos], OnePos :: non_neg_integer(), Result :: binary().

    Constructs a new binary by replacing the parts in Subject matching Pattern with Replacement if given as a literal binary/0 or with the result of applying Replacement to a matching subpart if given as a fun.

    If Replacement is given as a binary/0 and the matching subpart of Subject giving rise to the replacement is to be inserted in the result, option {insert_replaced, InsPos} inserts the matching part into Replacement at the specified position (or positions) before inserting Replacement into Subject. If Replacement is given as a fun instead, this option is ignored.

    If any position specified in InsPos is greater than the size of the replacement binary, a badarg exception is raised.

    Options global and {scope, part()} work as for split/3. The return type is always binary/0.

    For a description of Pattern, see compile_pattern/1.

  Examples

    1> binary:replace(<<"abcde">>, [<<"b">>, <<"d">>], <<"X">>, []).
    <<"aXcde">>
    2> binary:replace(<<"abcde">>, [<<"b">>, <<"d">>], <<"X">>, [global]).
    <<"aXcXe">>
    3> binary:replace(<<"abcde">>, <<"b">>, <<"[]">>, [{insert_replaced, 1}]).
    <<"a[b]cde">>
    4> binary:replace(<<"abcde">>, [<<"b">>, <<"d">>], <<"[]">>, [global,{insert_replaced,1}]).
    <<"a[b]c[d]e">>
    5> binary:replace(<<"abcde">>, [<<"b">>, <<"d">>], <<"[]">>, [global,{insert_replaced,[1,1]}]).
    <<"a[bb]c[dd]e">>
    6> binary:replace(<<"abcde">>, [<<"b">>, <<"d">>], <<"[-]">>, [global,{insert_replaced,[1,2]}]).
    <<"a[b-b]c[d-d]e">>
    7> binary:replace(<<"abcde">>, [<<"b">>, <<"d">>], fun(M) -> <<$[, M/binary, $]>> end, []).
    <<"a[b]cde">>
    8> binary:replace(<<"abcde">>, [<<"b">>, <<"d">>], fun(M) -> <<$[, M/binary, $]>> end, [global]).
    <<"a[b]c[d]e">>
split(Subject, Pattern, Options) -> Parts when Subject :: binary(), Pattern :: PatternBinary | [PatternBinary, ...] | cp(), PatternBinary :: nonempty_binary(), Options :: [Option], Option :: {scope, part()} | trim | global | trim_all, Parts :: [binary()].

    Splits Subject into a list of binaries based on Pattern.

    If option global is not specified, only the first occurrence of Pattern in Subject gives rise to a split.

    The parts of Pattern found in Subject are not included in the result.

    Summary of options: {scope, part()}
        Works as in match/3 and matches/3. Note that this only defines the scope of the search for matching strings; it does not cut the binary before splitting. The bytes before and after the scope are kept in the result. See the example below.
    trim
        Removes trailing empty parts of the result (as does trim in re:split/3).
    trim_all
        Removes all empty parts of the result.
    global
        Repeats the split until Subject is exhausted. Conceptually option global makes split work on the positions returned by matches/3, while it normally works on the position returned by match/3.

    Example of the difference between a scope and taking the binary apart before splitting:

        1> binary:split(<<"banana">>, [<<"a">>], [{scope,{2,3}}]).
        [<<"ban">>,<<"na">>]
        2> binary:split(binary:part(<<"banana">>,{2,3}), [<<"a">>], []).
        [<<"n">>,<<"n">>]

    The return type is always a list of binaries that are all referencing Subject. This means that the data in Subject is not copied to new binaries, and that Subject cannot be garbage collected until the results of the split are no longer referenced.

    For a description of Pattern, see compile_pattern/1.

  Examples

    1> binary:split(~"the quick brown fox", ~" ", []).
    [<<"the">>,<<"quick brown fox">>]
    2> binary:split(~"the quick brown fox", ~" ", [global]).
    [<<"the">>,<<"quick">>,<<"brown">>,<<"fox">>]
    3> binary:split(<<1,255,4,0,0,0,2,3>>, [<<0,0,0>>,<<2>>], []).
    [<<1,255,4>>, <<2,3>>]
    4> binary:split(<<0,1,0,0,4,255,255,9>>, [<<0,0>>, <<255,255>>], [global]).
    [<<0,1>>,<<4>>,<<9>>]