From: Ryan Pavlik <rpav@...>
Date: 2003-10-03T10:38:11+09:00
Subject: Re: backquotes, system, shell and ruby

On Fri, 3 Oct 2003 10:16:53 +0900
John Carter <john.carter@tait.co.nz> wrote:

> Somebody suggested I use zsh instead of bash for my commandline, so I
> looked at it, looked at the syntax for tweaking the profile files, and
> said...
> "Yuck! Another badly designed syntax! Why can't I just use Ruby?"

It's sh.  Deal with it. ;-) It's not great, but it's not so bad,
either.  I would, however, not mind having a ruby shell.  But I also
don't expect to use ruby---which is designed to be suitable primarily
as a programming language---to *directly* fit the bill.

> And that got me thinking.
> 
> Consider backquotes.
<snip> 
> Why? Why does a scripting language like Ruby keep invoking an old and bad
> scripting language call shell?

I'm not sure what you're getting at here.  Yes, it ran a shell,
because that's what system() does.  You can even do it in C, although
C doesn't use backticks as a shorthand.

> Because...
> 
>  a) Ruby doesn't have a good syntax for invoking and dealing with
>     processes and pipes between processes.

You mean like File.popen?

>  b) Ruby doesn't have a built in understanding of ENV['PATH']

The OS understands the path for you.  Ruby doesn't need to.

>  c) Ruby doesn't have such a simple syntax for globbing (beyond
>     Dir['*.c'])

Ruby isn't a shell, either, and although it is a scripting language
(which explains the presence of ``), this doesn't automatically make
it suitable for a drop-in shell replacement.

>     Consider the "rename" facility that comes with perl these days.
<snip>
>    Ooh! Looky! Nice! Wouldn't it be nice to have the power of ruby
>    intertwingled with the commandline.

At times I fire up irb to take care of similar complex tasks.

> Ruby does have Shell.rb, which takes us halfway there. (If it had
> decent docs...)
> 
> How hard would it be to extend the backtick syntax to be a pure ruby
> thing. ie. So proc_exec doesn't invoke bash, but invokes Shell.rb?
> 
> 
> Hmm. Could we even do this entirely in UserLand? ie. Couldn't we
> override proc_exec and replace it with ruby code that parses the
> string, handles the redirects, variable interpolation quoting and
> forks, then just directly execs the program without ever touching sh?

What you need to do is simply write a shell that uses ruby instead of
its own sh-like syntax.  Modifying ruby is not the answer.  Using ruby
and a little readline loop with some decent parsing (calls to fork,
popen, etc.: process and IPC handling) is.

I must say I have wanted something like this for awhile.  I even came
up with a really nice syntax for integrating shell commands and ruby,
although I forget off the top of my head what it was... it'd be
_fairly_ easy to do.

Just don't try to modify ruby to do it, because it's not the right
solution.

-- 
Ryan Pavlik <rpav@mephle.com>

"Well what was it, Mr. Nightmare Pants?" - 8BT