User's Guide
Reference Manual
Release Notes
PDF
Top

STDLIB
Reference Manual
Version 1.17.5

Expand All
Contract All

Table of Contents

# binary

### MODULE

binary

### MODULE SUMMARY

Library for handling binary data

### DESCRIPTION

This module contains functions for manipulating byte-oriented binaries. Although the majority of functions could be implemented using bit-syntax, the functions in this library are highly optimized and are expected to either execute faster or consume less memory (or both) than a counterpart written in pure Erlang.

The module is implemented according to the EEP (Erlang Enhancement Proposal) 31.

Note

The library handles byte-oriented data. Bitstrings that are not binaries (does not contain whole octets of bits) will result in a badarg exception being thrown from any of the functions in this module.

### DATA TYPES

cp()

Opaque data-type representing a compiled search-pattern. Guaranteed to be a tuple() to allow programs to distinguish it from non precompiled search patterns.

part() = {Start :: integer() >= 0, Length :: integer()}

A representaion of a part (or range) in a binary. Start is a zero-based offset into a binary() 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()'s with positive Length.

### EXPORTS

at(Subject, Pos) -> byte()

Types:

Subject = binary()
Pos = integer() >= 0

Returns the byte at position Pos (zero-based) in the binary Subject as an integer. If Pos >= byte_size(Subject), a badarg exception is raised.

bin_to_list(Subject) -> [byte()]

Types:

Subject = binary()

The same as bin_to_list(Subject,{0,byte_size(Subject)}).

bin_to_list(Subject, PosLen) -> [byte()]

Types:

Subject = binary()
PosLen = part()

Converts Subject to a list of byte()s, each representing the value of one byte. The part() denotes which part of the binary() to convert. Example:

    1> binary:bin_to_list(<<"erlang">>,{1,3}).
    "rla"
    %% or [114,108,97] in list notation.

If PosLen in any way references outside the binary, a badarg exception is raised.

bin_to_list(Subject, Pos, Len) -> [byte()]

Types:

Subject = binary()
Pos = integer() >= 0
Len = integer() >= 0

The same as bin_to_list(Subject,{Pos,Len}).

compile_pattern(Pattern) -> cp()

Types:

Pattern = binary() | [ binary() ]

Builds an internal structure representing a compilation of a search-pattern, later to be used in the match/3, matches/3, split/3 or replace/4 functions. The cp() returned is guaranteed to be a tuple() to allow programs to distinguish it from non pre-compiled search patterns

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

The list of binaries used for search alternatives shall be flat and proper.

If Pattern is not a binary or a flat proper list of binaries with length > 0, a badarg exception will be raised.

copy(Subject) -> binary()

Types:

Subject = binary()

The same as copy(Subject, 1).

copy(Subject,N) -> binary()

Types:

Subject = binary()
N = integer() >= 0

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

This function will always create a new binary, even if N = 1. By using copy/1 on a binary referencing a larger binary, one might free up the larger binary for garbage collection.

Note

By deliberately copying a single binary to avoid referencing a larger binary, one might, instead of freeing up the larger binary for later garbage collection, create much more binary data than needed. Sharing binary data is usually good. Only in special cases, when small parts reference large binaries and the large binaries are no longer used in any process, deliberate copying might be a good idea.

If N < 0, a badarg exception is raised.

decode_unsigned(Subject) -> Unsigned

Types:

Subject = binary()
Unsigned = integer() >= 0

The same as decode_unsigned(Subject,big).

decode_unsigned(Subject, Endianess) -> Unsigned

Types:

Subject = binary()
Endianess = big | little
Unsigned = integer() >= 0

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

Example:

    1> binary:decode_unsigned(<<169,138,199>>,big).
    11111111

encode_unsigned(Unsigned) -> binary()

Types:

Unsigned = integer() >= 0

The same as encode_unsigned(Unsigned,big).

encode_unsigned(Unsigned,Endianess) -> binary()

Types:

Unsigned = integer() >= 0
Endianess = big | little

Converts a positive integer to the smallest possible representation in a binary digit representation, either big or little endian.

Example:

    1> binary:encode_unsigned(11111111,big).
    <<169,138,199>>

first(Subject) -> byte()

Types:

Subject = binary()

Returns the first byte of the binary Subject as an integer. If the size of Subject is zero, a badarg exception is raised.

last(Subject) -> byte()

Types:

Subject = binary()

Returns the last byte of the binary Subject as an integer. If the size of Subject is zero, a badarg exception is raised.

list_to_bin(ByteList) -> binary()

Types:

ByteList = iodata() (see module erlang)

Works exactly as erlang:list_to_binary/1, added for completeness.

longest_common_prefix(Binaries) -> integer() >= 0

Types:

Binaries = [ binary() ]

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

    1> binary:longest_common_prefix([<<"erlang">>,<<"ergonomy">>]).
    2
    2> binary:longest_common_prefix([<<"erlang">>,<<"perl">>]).
    0

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

longest_common_suffix(Binaries) -> integer() >= 0

Types:

Binaries = [ binary() ]

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

    1> binary:longest_common_suffix([<<"erlang">>,<<"fang">>]).
    3
    2> binary:longest_common_suffix([<<"erlang">>,<<"perl">>]).
    0

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

match(Subject, Pattern) -> Found | nomatch

Types:

Subject = binary()
Pattern = binary() | [ binary() ] | cp()
Found = part()

The same as match(Subject, Pattern, []).

match(Subject,Pattern,Options) -> Found | nomatch

Types:

Subject = binary()
Pattern = binary() | [ binary() ] | cp()
Found = part()
Options = [ Option ]
Option = {scope, part()}

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

The function will return {Pos,Length} for the binary in Pattern starting at the lowest position in Subject, Example:

    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.

Summary of the options:

{scope, {Start, Length}}

  Only the given part is searched. Return values still have offsets from the beginning of Subject. A negative Length is allowed as described in the TYPES section of this manual.

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 given in the options such that Start is larger than the size of Subject, Start + Length is less than zero or Start + Length is larger than the size of Subject, a badarg exception is raised.

matches(Subject, Pattern) -> Found

Types:

Subject = binary()
Pattern = binary() | [ binary() ] | cp()
Found = [ part() ] | []

The same as matches(Subject, Pattern, []).

matches(Subject,Pattern,Options) -> Found

Types:

Subject = binary()
Pattern = binary() | [ binary() ] | cp()
Found = [ part() ] | []
Options = [ Option ]
Option = {scope, part()}

Works like match, but the 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 given raise to one more match,<<"de">>). This corresponds to the behavior of posix regular expressions (and programs like awk), but is not consistent with alternative matches in re (and Perl), where instead lexical ordering in the search pattern selects which string matches.

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

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

If {scope, {Start,Length}} is given in the options such that Start is larger than the size of Subject, Start + Length is less than zero or Start + Length is larger than the size of Subject, a badarg exception is raised.

part(Subject, PosLen) -> binary()

Types:

Subject = binary()
PosLen = part()

Extracts the part of the binary Subject described by PosLen.

Negative length can be used to extract bytes at the end of a binary:

    1> Bin = <<1,2,3,4,5,6,7,8,9,10>>.
    2> binary:part(Bin,{byte_size(Bin), -5}).
    <<6,7,8,9,10>>

Note

part/2and 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 PosLen in any way references outside the binary, a badarg exception is raised.

part(Subject, Pos, Len) -> binary()

Types:

Subject = binary()
Pos = integer() >= 0
Len = integer() >= 0

The same as part(Subject, {Pos, Len}).

referenced_byte_size(binary()) -> integer() >= 0

If a binary references a larger binary (often described as being a sub-binary), it can be useful to get the size of the actual referenced binary. This function can be used in a program to trigger the use of copy/1. By copying a binary, one might dereference the original, possibly large, binary which a smaller binary is a reference to.

Example:

    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 chose to copy the binary content before inserting it in the gb_set() if it references a binary more than twice the size of the data we're going to keep. Of course different rules for when copying will apply to different programs.

Binary sharing will occur whenever binaries are taken apart, this is the fundamental reason why binaries are fast, decomposition can always be done with O(1) complexity. In rare circumstances this data sharing is however undesirable, why this function together with copy/1 might be useful when optimizing for memory use.

Example of binary sharing:

    1> A = binary:copy(<<1>>,100).
    <<1,1,1,1,1 ...
    2> byte_size(A).
    100
    3> binary:referenced_byte_size(A)
    100
    4> <<_:10/binary,B:10/binary,_/binary>> = A.
    <<1,1,1,1,1 ...
    5> byte_size(B).
    10
    6> binary:referenced_byte_size(B)
    100

Note

Binary data is shared among processes. If another process still references the larger binary, copying the part this process uses only consumes more memory and will not free up the larger binary for garbage collection. Use this kind of intrusive functions with extreme care, and only if a real problem is detected.

replace(Subject, Pattern, Replacement) -> Result

Types:

Subject = binary()
Pattern = binary() | [binary()] | cp()
Replacement = Result = binary()

The same as replace(Subject,Pattern,Replacement,[]).

replace(Subject, Pattern, Replacement, Options) -> Result

Types:

Subject = binary()
Pattern = binary() | [binary()] | cp()
Replacement = binary()
Options = [Option]
Option = global | {scope, part()} | {insert_replaced, InsPos}
InsPos = OnePos | [OnePos]
OnePos = integer() >= 0
An integer() =< byte_size(Replacement)
Result = binary()

Constructs a new binary by replacing the parts in Subject matching Pattern with the content of Replacement.

If the matching sub-part of Subject giving raise to the replacement is to be inserted in the result, the option {insert_replaced, InsPos} will insert the matching part into Replacement at the given position (or positions) before actually inserting Replacement into the Subject. Example:

    1> binary:replace(<<"abcde">>,<<"b">>,<<"[]">>,[{insert_replaced,1}]).
    <<"a[b]cde">>
    2> binary:replace(<<"abcde">>,[<<"b">>,<<"d">>],<<"[]">>,
                     [global,{insert_replaced,1}]).
    <<"a[b]c[d]e">>
    3> binary:replace(<<"abcde">>,[<<"b">>,<<"d">>],<<"[]">>,
                     [global,{insert_replaced,[1,1]}]).
    <<"a[bb]c[dd]e">>
    4> binary:replace(<<"abcde">>,[<<"b">>,<<"d">>],<<"[-]">>,
                     [global,{insert_replaced,[1,2]}]).
    <<"a[b-b]c[d-d]e">>

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

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

For a description of Pattern, see compile_pattern/1.

split(Subject, Pattern) -> Parts

Types:

Subject = binary()
Pattern = binary() | [binary()] | cp()
Parts = [binary()]

The same as split(Subject, Pattern, []).

split(Subject, Pattern, Options) -> Parts

Types:

Subject = binary()
Pattern = binary() | [binary()] | cp()
Options = [Option]
Option = {scope, part()} | trim | global
Parts = [binary()]

Splits Subject into a list of binaries based on Pattern. If the option global is not given, only the first occurrence of Pattern in Subject will give rise to a split.

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

Example:

    1> binary:split(<<1,255,4,0,0,0,2,3>>, [<<0,0,0>>,<<2>>],[]).
    [<<1,255,4>>, <<2,3>>]
    2> binary:split(<<0,1,0,0,4,255,255,9>>, [<<0,0>>, <<255,255>>],[global]).
    [<<0,1>>,<<4>>,<<9>>]

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 will be kept in the result. See example below.

trim

  Removes trailing empty parts of the result (as does trim in re:split/3)

global

  Repeats the split until the Subject is exhausted. Conceptually the global option 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 actually 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.