Provided by: erlang-manpages_16.b.3-dfsg-1ubuntu2.2_all 
NAME
binary - 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()
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()
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()}
part() = {Start :: integer() >= 0, Length :: integer()}
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 DATA 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()}
part() = {Start :: integer() >= 0, Length :: integer()}
Works like match/2, 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()
The same as part(Subject, {Pos, Len}).
referenced_byte_size(Binary) -> integer() >= 0
Types:
Binary = binary()
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.