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From: avolio@decuac.dec.com (Frederick M. Avolio)
Newsgroups: comp.unix.questions
Subject: \"+\" filename -> /bin/sh !
Message-ID: <1761@decuac.DEC.COM>
Date: Tue, 20-Oct-87 12:59:03 EDT
Article-I.D.: decuac.1761
Posted: Tue Oct 20 12:59:03 1987
Date-Received: Thu, 22-Oct-87 00:26:11 EDT
References: <3351@sol.ARPA> <18062@teknowledge-vaxc.ARPA>
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In article <18062@teknowledge-vaxc.ARPA> mkhaw@teknowledge-vaxc.ARPA (Mike Khaw) writes:
>in article <3351@sol.ARPA>, ken@cs.rochester.edu (Ken Yap) says:

>> Since + is a non-binary, you are effectively doing /bin/sh +.  Try
>> this:
>> 	/bin/sh +
>> 
>> and get an interactive sh. In fact any argument starting with +
>> will get you the same result.
>On Ultrix 1.2, from either /bin/csh or /bin/sh I get:
>
>	+: +: cannot open
>

I am not sure what all the hubbub (haven't used THAT one in awhile,
eh?) is all about but it all depends on how arguments to the
particular shell are handled and what version of the shell, etc.  For
example, the System V r 2 Bourne Shell that comes with ULTRIX-32
(/bin/sh5) does indeed start up a subshell on your terminal as
originally discribed. 

The reason is that a '+' is allowed, similar to a '-' to turn on some
flags (see the manual page).  It goes into a piece of code which
affectively says:

	"sh +"
	Hmmmm...  let's parse those arguments...
		I see a '+'.  Let's go into a while loop, 
		turning on options as we go
			while options -- oops, no more options, bailout
		Now, for more arguements... Oh, no more. Drop through.
	Ok, I am ready... no file name so read from the tty

Now, admittedly, I am not sure that this is a Good Thing, but this is
*why* it happens and does not happen on all shells.  Depends on *which*
Bourne shell it is (v7?  SysVr2.0?  2.2?  SysVr3?) and how it is
written.

Fred