suetanvil / mruby-bin-monolith

Tool to "compile" mruby code into a standalone executable

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Create standalone executables from your MRuby scripts without a C/C++ toolchain.

How it works

The major operating systems' executable file formats all ignore data that has been appended to the file. This means that an executable with mrb data appended to it will work fine; the operating system loader will ignore it.

Monolith adds an executable (monolith_run) linked against MRuby (plus whatever mgems have been added) that

  1. finds its own executable
  2. opens it for reading and seeks ahead to the end of a special barrier string.
  3. sets up an mruby interpreter, and
  4. loads the rest of the executable into it as bytecodes and runs them.

So by appending one or more byte-compiled MRuby (.mrb) files to it, you can easily create a self-contained single file executable version of your MRuby program.


This gem creates two standalone tools, monolith and monolith_run. The latter can mostly be ignored but is documented below for completeness.


monolith is the build tool. Given one or more mruby source files on the command line, it will produce an executable:

$ echo 'puts "Hello!"' > a.rb
$ echo 'puts "World"' > b.rb
$ monolith a.rb b.rb
$ ./b

The executable's name is taken from the last input file. You can override this with the --output flag:

$ monolith a.rb b.rb --output hi
$ ./hi

It will also accept compiled mruby (.mrb) files:

$ monolith a.mrb b.mrb --output hi2
$ ./hi2

If your workflow centers around rapidly recompiling and running your program, you may benefit from the --execute option, which will execute the program after it has successfully been compiled:

$ monolith a.mrb b.mrb --execute

Option Reference

  • -v/--verbose
    • Display more messages.
  • -r/--runner PATH
    • Use the file at PATH instead of the default (a file named monolith_run in directory containing the monolith executable being run.)
  • -o/--output EXE
    • Write the output file to EXE instead of the default name.
  • -s/--strip
    • Run strip on a copy of monolith_run before appending the bytecodes. Some strips get confused by the trailing bytecodes so this is an easy way to ship stripped executables based on builds of monolith_run that still have debug symbols.
  • -c/--compiler PATH
    • Specify the compiler to use for bytecode-compiling mruby source code instead of the default (the mrbc located in the same directory as monolith).
  • -e/--execute
    • Execute the resulting program on success.


monolith_run is intended to be the start of a standalone mruby program. It opens its own executable, searches for a known barrier string and then treats everything following it as MRuby bytecodes. These are read and executed more or less the same way mruby would.

If run by itself with no arguments, it will print an error message and exit with a non-zero status.

If run with only the argument --print-barrier, it will output the barrier string that it searches for. This is used by monolith when assembling an executable.

Note that monolith_run does not do Unix-style argument parsing; --print-barrier is a special case. (So is --help.)

Finally, if monolith_run is run with one or more compiled MRuby (.mrb) files on the command line, it will load and run them. (This is probably not very useful.)


module Monolith

In a flagrant violation of the guideline against mixing extensions and tools, Monolith also provides a module (named Monolith) that adds a couple of items to the mruby environment. These are intended for development and/or debugging your compiled scripts.


  • Monolith.whereami() -> string

    • Returns the absolute path to the native-code executable being run. This invokes the same function monolith_run uses to find its own executable.
  • Monolith::IsApp -> boolean

    • true if the current program is a standalone compiled Ruby program; false otherwise. Constant.

Installation via mrbgems

Simply add this conf.gem line to build_config.rb: do |conf|

    # ... (snip) ...

    conf.gem :github => 'suetanvil/mruby-bin-monolith',
             :branch => 'main'

Note that this gem depends on a number of other external mrbgems which in turn end up importing most(?) of the core gembox. This will produce a featureful but large mruby build.


Released under the MIT License. See the LICENSE and AUTHORS files.


Tool to "compile" mruby code into a standalone executable



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