From: Eivind Eklund <eeklund@...>
Date: 2004-10-02T04:30:58+09:00
Subject: Re: Ruby as a shell (was Re: irb: a great tool in it's own right)

On Sat, 2 Oct 2004 00:09:59 +0900, Robert Klemme <bob.news@gmx.net> wrote:
> 
> "Eivind Eklund" <eeklund@gmail.com> schrieb im Newsbeitrag
> news:dc9b20bb041001065332408f65@mail.gmail.com...
> 
> > On the subject (if not the Subject:): Have anybody played with make it
> > possible to use Ruby for running sort-of shell scripts?
> 
> This topic arises from time to time.  AFAIR there are IRB extensions that
> make IRB shell-like.

I'm not thinking of IRB  - I'm thinking of scripting specifically.

> >  Ie, including
> > pipes etc.
> 
> IO.popen() uses pipes internally.  And I think there is also another
> method.

Yes, but these are highly clumsy when doing complex operations.

> >  As it is, there are some programs that call a lot of shell
> > commands that I write in sh instead of Ruby, and where I'd really like
> > to do them in Ruby.
> 
> Depending on what you do, you might notice that you don't need those shell
> programs for the job.  For example, "cat" is easily done with File.open()
> {|io|...} and "rm" can be taken care of by File.delete().

I know, but again: This does not handle the cases I'm interested in.  

> > The starting point I see for something like this would be to override
> > method_missing like above, but make it return an object where | is
> > overridden, and that have handling of shell return codes.
> >
> > The challenges I see here is
> > - It's not possible to override the trueness/falseness of an object,
> > so we'd need to call a special method to find out if a command failed
> > or passed
> > - It is hard to implement -e (give an error if a complete shell line
> > fails - but not if we have an fail || true).  Maybe trace_func could
> > be of help here, though.
> 
> I'm not sure whether I wanted Ruby scripts to look similar to shell
> scripts or whether it's feasible to a degree that is satisfactory.

I don't want all Ruby programs to look like shell scripts.  However, I
find the shell script syntax very convenient for some types of
operations - more convenient than Ruby for programs where the chief
operations are running external commands with pipes and filters.  I
would like to be able to embed this into Ruby programs, and easily
convert this kind of program from a shell script to Ruby for further
massaging.

So yes, I really want an sh-like syntax inside my Ruby scripts - not
for everything, but for the cases where I presently end up using sh
because Ruby is inconvenient.

> I wouldn't mind having a method pipe(*commands) in Kernel or IO that starts
> all these commands in parallel and connects them via pipes.

Intriguing idea.  I'd use an array per command instead of a string (to
avoid white space parsing issues), but apart from that I like it :-)

It isn't quite what I'm thinking of, but it is more useful for the
general case.  (I was thinking of something for very special cases,
only usable inside particular blocks.)

Eivind.