From: gwtmp01@...
Date: 2005-06-24T03:31:58+09:00
Subject: Re: Shell type

On Jun 23, 2005, at 10:44 AM, Panich, Alexander wrote:
> Under Linux, by default, method Kernel.system(command) (backticks as
> well) executes command in the subshell of SH type.
>
> Is there a way to define another shell type (CSH for example) to  
> execute
> there, or not?
>

Ruby is just providing an interface to the system() function defined by
Posix, which defines system() to use "sh".

There are two general options then:

Use system() to run "sh" to run your interpreter:

     system('/bin/csh mycshellscript')

or drop down a level and use Kernel#exec which interacts directly with
the exec() family of system calls.  Once you decide to do this, you
probably have to start understanding how to use fork/exec together
because exec by itself *replaces* the current running process.  If you
execute (in Ruby)

     exec "date"

Then the ruby interpreter will be discarded by the current process and
replaced with the /bin/date program, which will do it's thing and then
exit.  Instead you would probably want

     fork { exec "date" }

which will cause the ruby process to fork.  The new (child) process
(Ruby) will then execute the block and be immediately replaced with the
date executable when the Ruby interpreter calls the exec() system
call. Meanwhile the original Ruby process continues executing.  There
are more details of course if you want the parent process to wait for
the child and such.  This is all Unix system programming stuff that
Ruby provides via the Kernel and Process classes.

There are lots of details to consider with exec to setup environment
variables, argument lists, and what directories to search for the
executable. See Kernel#exec or the man pages for the exec family of
functions (execl/execlp/execle, etc.)

If you haven't worked with fork/exec calls before they can be
a little disorienting because of the way things are shared between
the processes (fork) or programs (exec).



Gary Wright