beam_lib(3)

MODULE
beam_lib - An interface to the BEAM file format

DESCRIPTION

beam_lib provides an interface to files created by the BEAM compiler ("BEAM files"). The format used, a variant of "EA IFF 1985" Standard for Interchange Format Files, divides data into chunks.

Chunk data can be returned as binaries or as compound terms. Compound terms are returned when chunks are referenced by names (atoms) rather than identifiers (strings). The names recognized and the corresponding identifiers are abstract_code ("Abst"), attributes ("Attr"), exports ("ExpT"), labeled_exports ("ExpT"), imports ("ImpT"), locals ("LocT"), labeled_locals ("LocT"), and atoms ("Atom").

The syntax of the compound term (ChunkData) is as follows:

    *   ChunkData = {ChunkId, binary()} | {abstract_code, AbstractCode} | {attributes, [{Attribute, [AttributeValue]}]} | {exports, [{Function, Arity}]} | {labeled_exports, [{Function, Arity, Label}]} | {imports, [{Module, Function, Arity}]} | {locals, [{Function, Arity}]}]} | {labeled_locals, [{Function, Arity, Label}]}]} | {atoms, [{integer(), atom()}]}

    *   ChunkRef = ChunkId | ChunkName

    *   ChunkName = abstract_code | attributes | exports | imports | locals

    *   ChunkId = string()

    *   AbstractCode = {AbstVersion, forms()} | no_abstract_code

    *   AbstVersion = atom()

    *   Attribute = atom()

    *   AttributeValue = term()

    *   Module = Function = atom()

    *   Arity = integer() >= 0

    *   Label = integer() >= 0

The list of attributes is sorted on Attribute, and each attribute name occurs once in the list. The attribute values occur in the same order as on the file. The lists of functions are also sorted. It is not checked that the forms conform to the abstract format indicated by AbstVersion.

no_abstract_code means that the "Abst" chunk is present, but empty.

Each of the functions described below accept either a filename or a binary containing a beam module.

EXPORTS

chunks(FileNameOrBinary, [ChunkRef]) -> {ok, {Module, [ChunkData]}} | {error, Module, Reason}

    Types
        FileNameOrBinary = string() | atom() | binary()
        Reason = {unknown_chunk, FileName, atom()} | - see info/1 -

    The chunks/2 function reads chunk data for selected chunks. The order of the returned list of chunk data is determined by the order of the list of chunks references; if each chunk data were replaced by the tag, the result would be the given list.

version(FileNameOrBinary) -> {ok, {Module, Version}} | {error, Module, Reason}

    Types
        FileNameOrBinary = string() | atom() | binary()
        Version = [term()]
        Reason = - see chunks/2 -

    The version/1 function returns the module version(s) found in a BEAM file.

info(FileNameOrBinary) -> [SourceRef, {module, Module}, {chunks, [ChunkInfo]}] | {error, Module, Reason}

    Types
        FileName = string() | atom()
        FileNameOrBinary = FileName | binary()
        SourceRef = {file, FileName} | {binary, binary()}
        ChunkInfo = {ChunkId, StartPosition, Size}
        StartPosition = integer() > 0
        Size = integer() >= 0
        Reason = {chunk_too_big, FileName, ChunkId, ChunkSize, FileSize} | {invalid_beam_file, FileName, FilePosition} | {invalid_chunk, FileName, ChunkId} | {missing_chunk, FileName, ChunkId} | {not_a_beam_file, FileName} | {file_error, FileName, FileError}

    The info/1 function extracts some information about a BEAM file: the file name, the module name, and for each chunk the identifier as well as the position and size in bytes of the chunk data.

cmp(FileNameOrBinary, FileNameOrBinary) -> ok | {error, Module, Reason}

    Types
        FileName = string() | atom()
        FileNameOrBinary = FileName | binary()
        Reason = {modules_different, Module, Module} | {chunks_different, ChunkId} | - see info/1 -

    The cmp/2 function compares the contents of two BEAM files. If the module names are the same, and the chunks with the identifiers "Code", "ExpT", "ImpT", "StrT", and "Atom" have the same contents in both files, ok is returned. Otherwise an error message is returned.

cmp_dirs(Directory1, Directory2) -> {Only1, Only2, Different} | {error, Module, Reason}

    Types
        Directory1 = Directory2 = string() | atom()
        Different = [{FileName1, FileName2}]
        Only1 = Only2 = [FileName]
        FileName = FileName1 = FileName2 = string()
        Reason = - see info/1 -

    The cmp_dirs/2 function compares the BEAM files in two directories. Only files with extension ".beam" are compared. BEAM files that exist in directory Directory1 (Directory2) only are returned in Only1 (Only2). BEAM files that exist on both directories but are considered different by cmp/2 are returned as pairs {FileName1, FileName2} where FileName1 (FileName2) exists in directory Directory1 (Directory2).

diff_dirs(Directory1, Directory2) -> ok | {error, Module, Reason}

    Types
        Directory1 = Directory2 = string() | atom()
        Reason = - see info/1 -

    The diff_dirs/2 function compares the BEAM files in two directories the way cmp_dirs/2 does, but names of files that exist in only one directory or are different are presented on standard output.

strip(FileNameOrBinary) -> {ok, {Module, FileNameOrBinary}} | {error, Module, Reason}

    Types
        FileName = string() | atom()
        FileNameOrBinary = FileName | binary()
        Reason = - see info/1 -

    The strip/1 function removes all chunks from a BEAM file except those needed by the loader. In particular, the abstract code is removed. The module name found in the file and the file name, possibly with the ".beam" extension added, are returned.

strip_files(Files) -> {ok, [{Module, FileNameOrBinary]}} | {error, Module, Reason}

    Types
        Files = [FileNameOrBinary]
        FileName = string() | atom()
        FileNameOrBinary = FileName | binary()
        Reason = - see info/1 -

    The strip_files/1 function removes all chunks except those needed by the loader from BEAM files. In particular, the abstract code is removed. The returned list contains one element for each given file name, ordered as the given list. The list element is a pair of the module name found in the file and the file name, the latter possibly with the ".beam" extension added.

strip_release(Directory) -> {ok, [{Module, FileName]}} | {error, Module, Reason}

    Types
        Directory = string() | atom()
        FileName = string()
        Reason = - see info/1 -

    The strip_release/1 function removes all chunks except those needed by the loader from the BEAM files of a release. Directory should be the installation root directory. For example, the current OTP release can be stripped with the call beam_lib:strip_release(code:root_dir()). The returned list contains module names and file names of stripped files.

format_error(Error) -> character_list()

    Given the error returned by any function in this module, the function format_error returns a descriptive string of the error in English. For file errors, the function format_error/1 in the file module is called.

AUTHOR
Hans Bolinder - support@erlang.ericsson.se