# beam_lib

### MODULE

beam_lib

### MODULE SUMMARY

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 | labeled_exports | imports | locals | labeled_locals | atoms`
- `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.

### AUTHORS

Hans Bolinder - support@erlang.ericsson.se

stdlib 1.12
Copyright © 1991-2003 Ericsson Utvecklings AB