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From: dalem@hpfcph.UUCP
Newsgroups: comp.unix.questions
Subject: Re: VMS shell under Unix (was: Re: why learn UNIX)
Message-ID: <3700003@hpfcph.HP.COM>
Date: Fri, 23-Jan-87 16:57:36 EST
Article-I.D.: hpfcph.3700003
Posted: Fri Jan 23 16:57:36 1987
Date-Received: Thu, 29-Jan-87 06:12:37 EST
References: <3353@bu-cs.BU.EDU>
Organization: HP Ft. Collins
Lines: 30

[discussion of emulators on various systems, etc.]

I guess I didn't make my point clearly enough.  I said that one could 
write a shell similar to DCL to run on UNIX quite easily, but writing a
shell similar to sh or csh to run on VMS would be tough.  Note that I did
NOT say it would be impossible.  One of the major differences between the
two systems is that with one system you only have to edit /etc/passwd and 
put the name of the shell in; under the other one you must modify 
sys$system:sysuaf.dat, install the shell in some special place, etc.  Note
that this process is not documented (or if it is, it is *well* hidden).

Another thing to keep in mind has already been mentioned - VMS is slow in
doing an equivalent of a fork()/exec() - something that is pretty fundamental
to a shell.  If one looks at the microfiche source for DCL, they are using
an undocumented call to run programs.  If you call DEC and ask about it, they
will deny its existence.  This leaves Joe Hacker with the choice of LIB$SPAWN
or SYS$CREPRC for doing his fork()/exec().  Both are horribly slow.

Note that this information is a few months old - it dates back to Spring 1986,
VAX/VMS V4.2.

Someone noted that one reason there are no VMS emulators on UNIX is that noone
would want one.  A *very* good point.  VMS has some nice features (a good 
backup/restore facility, the ability to rename a directory as a Joe User, the
ability to refer to the current directory and everything below it, etc.), but
has some pretty fundamental problems.

						Dale McCluskey

						{hplabs,ihnp4}!hpfcla!dalem