Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!bloom-beacon!ai-lab!tmb
From: tmb@wheaties.ai.mit.edu (Thomas M. Breuel)
Newsgroups: gnu.emacs
Subject: Re: Why programs use the shell to start up a program
Message-ID: <1273@rice-chex.ai.mit.edu>
Date: 24 Mar 89 13:05:04 GMT
References: <8903231435.AA11955@galaxy.compass.com>
Distribution: gnu
Organization: MIT AI Lab, Cambridge, MA
Lines: 17
In-reply-to: think!compass!worley@EDDIE.MIT.EDU's message of 23 Mar 89 14:35:49 GMT

In article <8903231435.AA11955@galaxy.compass.com> think!compass!worley@EDDIE.MIT.EDU (Dale Worley) writes:

   Generally the Un*x convention is that if a program wants to start an
   inferior process, it has the shell do it, rather than doing a fork()
   and exec() itself.  See, for example, the system() call.  You might
   well wonder why this is done, since it costs time, and probably sets
   up an additional process (is that really true?).  The reason is that
   often the "program name" to run is obtained from the user or an
   environment variable, and using the shell to process it gives
   additional flexibility.

People often complain that making a subshell is slow. This is mostly
a function of the kind of shell you are using. Using the Bourne shell
(at least for subshells), system() calls and subshells start up almost
instantaneously. If you must use the C-shell, you should at least check
in your .cshrc whether the shell is run interactively and skip most of
the .cshrc file if it is not.