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Amalg -- Amalgamation of Lua Modules/Scripts

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Deploying a Lua application that is split among multiple modules is a challenge. A tool that can package a Lua script and its modules into a single file is a valuable help. This is such a tool.


  • Pure Lua (compatible with Lua 5.1 and up), no other external dependencies (plugins may have external dependencies).
  • Even works for modules using the deprecated module function.
  • You don't have to take care of the order in which the modules are require'd.
  • Can embed compiled C modules.
  • Can collect require'd Lua (and C) modules automatically.
  • Can compress/decompress or precompile using plugin modules.

What it doesn't do:

  • It doesn't do static analysis of Lua code to collect require'd modules. That won't work reliably anyway. You can write your own program for that (using the output of luac -p -l), or use squish, or soar instead.
  • It doesn't handle the dependencies of C modules, so it is best used on C modules without dependencies (e.g. LuaSocket, LFS, etc.) or with statically linked C modules.

There are alternatives to this program: See squish, soar, luac.lua, luacc, many2one, and bundle.lua (and probably some more).

Getting Started

You can bundle a collection of modules in a single file by calling the amalg.lua script and passing the module names on the command-line.

./amalg.lua module1 module2

The modules are collected using package.path, so they have to be available there. You can use the usual environment variables (e.g. LUA_PATH) to adjust the contents of package.path. The resulting merged Lua code will be written to the standard output stream. You have to run the code to make the embedded Lua modules available for require.

You can specify an output file to use instead of the standard output stream.

LUA_PATH="../src/?.lua;;" ./amalg.lua -o out.lua module1 module2

You can also embed the main script of your application in the merged Lua code as well. Of course the embedded Lua modules can be require'd in the main script. The main script is specified as a filename or path, not a module name (it isn't a module after all). (It could be a module, but in that case the amalgamation file has to be require'd before the other embedded modules become available!)

lua amalg.lua -o out.lua -s main.lua module1 module2

If you want the original filenames and line numbers to appear in error messages, you have to activate debug mode. This will require slightly more memory, however.

./amalg.lua -o out.lua -d -s main.lua module1 module2

To collect all Lua (and C) modules used by a program, you can load the amalg.lua script as a module, and it will intercept calls to require and save the necessary Lua module names in a file amalg.cache in the current directory.

lua -lamalg main.lua

Multiple runs will add to this module cache. But don't access it from multiple concurrent processes!

You can use the cache (in addition to all module names given on the command-line) using the -c flag.

./amalg.lua -o out.lua -s main.lua -c

To use a custom file as cache specify -C <file>:

./amalg.lua -o out.lua -s main.lua -C myamalg.cache

However, this will only embed the Lua modules. To also embed C modules (both from the cache and from the command-line), you have to specify the -x flag:

./amalg.lua -o out.lua -s main.lua -c -x

This will make the amalgamated script platform and Lua version dependent, obviously! And it will not embed any external shared libraries that those modules might depend on. If your compiled C modules do have external dependencies, your best bet is to bundle the DLLs with the amalgamated Lua script (on Windows) or install the required dependencies on the target machine using the OSes package manager (e.g. on Linux).

In some cases you may want to ignore automatically listed modules in the cache without editing the cache file. Use the -i option for that and specify a Lua pattern:

./amalg.lua -o out.lua -s main.lua -c -i "^luarocks%."

The -i option can be used multiple times to specify multiple patterns.

Usually, the amalgamated modules take precedence over locally installed (possibly newer) versions of the same modules. If you want to use local modules when available and only fall back to the amalgamated code otherwise, you can specify the -f flag.

./amalg.lua -o out.lua -s main.lua -c -f

This installs another searcher/loader function at the end of the package.searchers (or package.loaders on Lua 5.1) and adds a new table package.postload that serves the same purpose as the standard package.preload table.

To fix a compatibility issue with Lua 5.1's vararg handling, amalg.lua by default adds a local alias to the global arg table to every loaded module. If for some reason you don't want that, use the -a flag (but be aware that in Lua 5.1 with LUA_COMPAT_VARARG defined (the default) your modules can only access the global arg table as _G.arg).

./amalg.lua -o out.lua -a -s main.lua -c

There is also some compression/decompression support handled via plugins to amalg. To select a compression plugin by name use the -z option. The necessary decompression code typically is embedded in the result and executed automatically at runtime (may depend on the plugin).

./amalg.lua -o out.lua -s main.lua -c -z brieflz

Some plugins generate valid Lua code (text or binary) and thus don't need a decompression step. For those modules the -t option should be used instead to avoid embedding no-op decompression code in the final amalgamation file. Multiple compression/transformation steps are possible, and they are executed in the given order.

./amalg.lua -o out.lua -s main.lua -c -t luasrcdiet -t luac -z brieflz

Note that compression is usually most effective when applied to the complete amalgamation script instead of just individual modules:

./amalg.lua -s main.lua -c | ./amalg.lua -o out.lua -s- -t luasrcdiet -z brieflz

Transformation plugins can also be used for transpiling some Lua dialect to plain Lua code during amalgamation. But plugins cannot modify the shebang line of the resulting script, so you should set one yourself if your main script contains one unsuitable for plain Lua code:

./amalg.lua -o out.lua -s main.moon -S "/usr/bin/env lua" -c -t moonscript

If you want to bundle some other read-only files with your amalgamated script, you can do so with virtual IO and the -v switch:

./amalg.lua -s main.lua -c -v template.txt

This will embed template.txt in the amalgamated script and monkey-patch the file IO functions if (and only if) the resource is opened read-only. This command-line switch may be used multiple times for multiple virtual resources. The file path has to match exactly or else normal file IO is used.

./amalg.lua -h

will list all available options (most options are also available as long options).

That's it. For further info consult the source (there's a nice annotated HTML file rendered with Docco on the GitHub pages). Have fun!


amalg.lua uses two kinds of plugins: transformation plugins and compression plugins. Transformation plugins are Lua modules that are called only during amalgamation. Compression plugins consist of two separate Lua modules that are called during amalgamation and at runtime to undo the modifications made during amalgamation, respectively. Since transformation plugins don't have a reverse transformation step, they are expected to produce valid Lua code (or Lua binary code). They are used only on pure Lua files (modules or main script). Compression plugins on the other hand are used on both Lua files and compiled C modules.

A transformation plugin (used with the command-line option -t <name>) is implemented as a Lua module amalg.<name>.transform. The module exports a function that takes a string (the input source), a boolean (whether the input source is in Lua source code format), and the original file path as arguments. It must return a string (the transformed input) and a boolean indicating whether the result is Lua source code. It is good practice to handle the case where the input is not in Lua source code format (but Lua binary code) by skipping the transformation in this case.

A compression plugin (used with the command-line option -z <name>) is implemented as two separate Lua modules amalg.<name>.deflate and amalg.<name>.inflate. The deflate part of the plugin works exactly like a transformation plugin module. It is called during amalgamation and may freely use external dependencies. The inflate module should be implemented as a self-contained pure Lua module as it is embedded into the amalgamation for the decompression step during runtime. This module exports a function taking the compressed input as a string and returning the decompressed output as string as well.

There are currently a few predefined plugins available:

luac Plugin

The luac plugin is a transformation plugin that compiles Lua source code into stripped Lua binary code. It doesn't have any external dependencies and passes through binary input (i.e. already compiled Lua code) unmodified. Note that binary Lua code may be larger than Lua source code, especially when encoded in Lua's decimal escape notation. Binary Lua code is also platform dependent. It may or may not load faster than regular Lua source code. It might make sense to additionally precompile the entire amalgamated result using luac because you otherwise still depend on Lua source code lexer and parser, and compressed/binary code in the amalgamated script is bigger than it needs to be because of the Lua decimal escape notation.

luasrcdiet Plugin

The luasrcdiet plugin is a transformation plugin that minifies Lua source code by replacing names of local variables, stripping white space, removing comments, etc. It passes through binary input (i.e. already compiled Lua code) unmodified. You need to install the luasrcdiet module for the amalgamation step. The amalgamated script doesn't have any extra dependencies. This transformation is a good choice for reducing the size of the resulting amalgamated Lua script.

dumbluaparser Plugin

The dumbluaparser transformation plugin is a more recent alternative to the luasrcdiet plugin, and also minifies Lua source code. It may work better with Lua 5.4-specific source code. As the name implies, the DumbLuaParser module has to be available during amalgamation.

brieflz Plugin

The brieflz plugin is a compression plugin that compresses its input during amalgamation and decompresses it on the fly during runtime. The compression step relies on the brieflz module which must be available during amalgamation. The decompression step is performed by a pure Lua port of the blz_depack_safe function from the original C code by Jørgen Ibsen (@jibsen). The decompression code is embedded into the resulting amalgamation script, so no extra dependency is needed at runtime, but it adds about 2kB (1kB when minified with luasrcdiet) size overhead. Note that binary data in the amalgamation is stored in standard Lua decimal escape notation, so it may be larger than usual. However, brieflz compression still reduces the size of the resulting amalgamation script in many cases, and you could precompile the result using the luac program (Lua bytecode doesn't need decimal escape notation).

moonscript Plugin

The moonscript plugin extends package.path when it is first loaded to search for .moon files in the same directories as for .lua files. .moon files take precedence. Then the plugin translates all non-binary modules and scripts from moonscript code to Lua code during amalgamation if the filename of the module or script ends in .moon. The Lua modules of the moonscript compiler are used for this translation, so it needs to be installed for the amalgamation step. Transformation plugins don't have a way to change the shebang lines of the amalgamated script, so you'll have to do that by hand if necessary using the -S/--shebang option. This plugin is well-behaved in the sense that it checks the file extension, so you can mix moonscript code, plain Lua code, and code for other well-behaved transpiler plugins in one amalgamation.

teal Plugin

The teal plugin works in a similar way as the moonscript plugin, but it searches for and processes .tl files. The tl module is used for the source code transformation, so it must be available during amalgamation.

fennel Plugin

The fennel plugin works in a similar way as the moonscript and tl plugin, but it searches for and processes .fnl files. The fennel module is used for the source code transformation, so it must be available during amalgamation.


amalg.lua does not find modules in the cache file generated via lua -lamalg

lua -lamalg records the module names exactly as they are used (required) by the application. Therefore, you should always tweak package.path instead of "fixing" the cache file if a module can't be found during amalgamation. This can happen if the application modifies its own package.path at runtime or changes its working directory.

My environment does not support require or the package module!

That's unfortunate. This tool relies on a working require function and a minimal package module. See this Stack Overflow post for how you can provide minimal stubs for the World of Warcraft environment. If you can't provide a shared require (and package) implementation in your environment, you can use the -p <file> switch to embed one very early in the amalgamation. Obviously this may cause problems if multiple scripts use this technique, so a common, shared approach is preferred.


Philipp Janda, siffiejoe(a)

Comments and feedback are always welcome.


amalg is copyrighted free software distributed under the MIT license (the same license as Lua 5.1). The full license text follows:

amalg (c) 2013-2021 Philipp Janda

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.