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From: simon@its63b.ed.ac.uk (Simon Brown)
Newsgroups: comp.unix.wizards
Subject: Re: symbolic links  and csh execution
Message-ID: <500@its63b.ed.ac.uk>
Date: Thu, 25-Jun-87 07:20:31 EDT
Article-I.D.: its63b.500
Posted: Thu Jun 25 07:20:31 1987
Date-Received: Sat, 4-Jul-87 17:34:51 EDT
References: <a7879@brl-adm.ARPA>> <2211@bunker.UUCP> <1097@mtune.ATT.COM> <21681@sun.uucp>
Reply-To: simon@its63b.ed.ac.uk (Simon Brown)
Organization: Computer Science Department, Edinburgh University
Lines: 53

In article <21681@sun.uucp> guy%gorodish@Sun.COM (Guy Harris) writes:
>The intent behind "#!"  was to permit *arbitrary* interpreters to run
>programs, not just shells.  (It also permits interpreted programs to
>be set-UID, assuming you trust the interpreter's mechanisms to the
>degree necessary to make set-UID interpeted programs safe.  Prior to
>4.3BSD, there were two very large security holes that rendered
>set-UID shell scripts, at least, unsafe; those two holes were closed
>in 4.3BSD, but there could well be others.)
>
>Huh?  How does "#!" "automagically" support "...a language processor
>which is a partial superset of an existing standard"?  What it
>supports is executing shell scripts as ordinary programs *without*
>having to ensure that all programs that might try to execute that
>script use "exec[lv]p" instead of "exec[lv]".  The latter is somewhat
>nice, considering that not all programs *do* use "exec[lv]p".
>

Unfortunately, execution of a "program" only makes sense from within an
interpreter environment (such as sh, csh, ...). After all, the command
"/bin/cat" that gets executed by a "#!/bin/cat" interpreter could have
widely different interpretations depending on who is executing it.
Luckily, all shells treat pathname-commands as being "execv that pathname",
but this does limit the sort of commands that may be issued via a
#! directive. 

I would quite like to use pipes, i/o redirection, shell-variables, etc... in
a #! - for example
	#!(sed 1d | tbl | nroff -ms | lpr)
	.PP
	Hello.
	.TS
	a table
	.TE
	[etc...]
in a file, to automatically run its contents through "tbl" and "nroff" and
print out the result, whenever the file is executed.
But there is no provision for this sort of syntax in a #!, which is a pity.

I guess ``#!/bin/sh -c "sed -d $1 | tbl | nroff -ms | lpr"'' might work,
but this is very ugly.

	%{
	    Simon.
	%}


-- 
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| Simon Brown                    | UUCP:  seismo!mcvax!ukc!its63b!simon
| Department of Computer Science | JANET: simon@uk.ac.ed.its63b
| University of Edinburgh,       | ARPA:  simon%its63b.ed.ac.uk@cs.ucl.ac.uk
| Scotland, UK.                  |
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