.BEAM

Introduction

A .beam file holds one compiled module for BEAM, the virtual machine of Erlang/OTP. The Erlang compiler writes one file per module, and so do the compilers of other languages that run on the same virtual machine, such as Elixir and Gleam. The runtime loads modules from these files as the program calls them, and can load a new version of a module while the system is running.

Structure

A BEAM file uses the chunk layout of the IFF format. It starts with FOR1, a 32-bit big-endian size for the rest of the file, and the form type BEAM. Then come chunks, each a four-character ID, a 32-bit big-endian length and that many bytes, padded to a multiple of four.

Common chunks are AtU8 (the atoms the module uses, in UTF-8; Atom in older files), Code (the bytecode), StrT (strings), ImpT, ExpT and LocT (imported, exported and local functions), LitT (literals), FunT (anonymous functions), Attr and CInf (module attributes and compiler information), Line (line numbers) and Dbgi or Docs for debug information and documentation.

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