Ed Gallagher wrote:
> Wondering if possible to compile a ruby script to byte code that can be
> executed in command line just as a .rb

Short answer: No, it doesn't.

(Slightly) longer answer: No, *Ruby* doesn't support storing and
loading bytecode, but most Ruby *Implementations* do. IOW: it's not
part of the Ruby Language Specification, but most Ruby Implementations
support it anyway. However, each Implementation has its own bytecode,
its own archive format and its own APIs. And, of course, some
implementations don't even *have* bytecode, so it's obviously
impossible for them to support bytecode loading.

(Much too) long answer: There is no portable bytecode specification
for Ruby, and thus also no standard way to load precompiled bytecode
archives. However, almost all Ruby implementations use some kind of
bytecode or intcode format, and several of them can dump and reload
bytecode archives.

YARV (<http://Ruby-Lang.Org/>) always compiles to bytecode before
executing the code, however that is usually only done in memory. There
are ways to dump out the bytecode to disk and to read it back *in*
(<https://GitHub.Com/Ruby/Ruby/blob/trunk/iseq.c#L438-534>).

Rubinius (<http://Rubini.us/>) also always compiles to bytecode, and
it has a format for compiled files
(<https://GitHub.Com/EvanPhx/Rubinius/blob/master/lib/compiler/compiled_file.rb>)
('.rbc' files, analogous to JVM '.class' files).

XRuby (<http://XRuby.GoogleCode.Com/>) is a pure compiler, it compiles
Ruby sourcecode straight to JVM bytecode ('.class' files). You can
deploy these '.class' files just like any other Java application.

JRuby (<http://JRuby.Org/>) started out as an interpreter, but it has
both a JIT compiler and an AOT compiler
(<https://GitHub.Com/JRuby/JRuby/tree/master/src/org/jruby/compiler/>)
('jrubyc') that can compile Ruby sourcecode to JVM bytecode ('.class'
files). Also, work is underway to create a *new*
(<https://GitHub.Com/JRuby/JRuby/blob/master/tool/compiler2.rb>)
compiler that can compile (type-annotated) Ruby code to JVM bytecode
that actually looks like a Java class and can be used from Java code
without barriers.

Ruby.NET (<http://RubyDotNETCompiler.GoogleCode.Com/>) is a pure
compiler that compiles Ruby sourcecode to CIL bytecode (PE '.dll' or
'.exe' files). You can deploy these just like any other CLI
application.

MacRuby (<http://MacRuby.Org/>) doesn't allow you to compile to 
bytecode, but it allows you to compile to *native* code.

IronRuby (<http://IronRuby.Net/>) also compiles to CIL bytecode, but
typically does this in-memory. However, you can pass commandline
switches
(<https://GitHub.Com/IronRuby/IronRuby/blob/master/Languages/Ruby/Ruby/Hosting/RubyOptionsParser.cs#L419-420>)
to it, so it dumps the '.dll' and '.exe' files out to disk. Once you
have those, they can be deployed normally, just like any other PE 
executable wherever you have an installation of .NET or Mono.

BlueRuby
(<https://SDN.SAP.Com/irj/scn/wiki?path=/display/Research/BlueRuby>)
automatically pre-parses Ruby sourcecode into BRIL (BlueRuby
Intermediate Language), which is basically a serialized parsetree.
(See *Blue Ruby - A Ruby VM in SAP ABAP*
(<https://SDN.SAP.Com/irj/scn/go/portal/prtroot/docs/library/uuid/408a9a3b-03f9-2b10-b29c-f0a3374b19d8>)
for details.)

I *think* (but I am definitely not sure) that there is a way to get
Cardinal (<https://GitHub.Com/Cardinal/Cardinal/>) to dump out Parrot
(<http://ParrotCode.Org/>) bytecode archives (PBC). (Actually,
Cardinal only compiles to PAST, and then Parrot takes over, so it
would be Parrot's job to dump and load bytecode archives.)

MRI doesn't have a bytecode.

HotRuby (<http://HotRuby.Accelart.Jp/>) and Red Sun
(<https://GitHub.Com/JonathanBranam/RedSun/>) appear to have the same
bytecode format as YARV, and they appear to be able to load bytecode,
but I am not familiar with them and can't make a definitive statement.

I am not familiar enough with tinyrb
(<http://Code.MACournoyer.Com/tinyrb/>), RubyGoLightly 
(<http://Feyeleanor.GitHub.Com/RubyGoLightly/>), SmallRuby
(<http://SWING.FIT.CVUT.Cz/projects/smallruby/>) or MagLev
(<http://MagLev.GemStone.Com/>) to make any statement about them.

jwm