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From: levy@ttrdc.UUCP (Daniel R. Levy)
Newsgroups: comp.unix.wizards
Subject: Re: #! magic number
Message-ID: <1792@ttrdc.UUCP>
Date: Tue, 30-Jun-87 19:04:54 EDT
Article-I.D.: ttrdc.1792
Posted: Tue Jun 30 19:04:54 1987
Date-Received: Thu, 2-Jul-87 03:33:31 EDT
References: <a7879@brl-adm.ARPA>> <2211@bunker.UUCP> <1097@mtune.ATT.COM> <488@quacky.UUCP>
Organization: AT&T, Skokie, IL
Lines: 63
Summary: don't be silly

In article <488@quacky.UUCP>, dce@mips.UUCP (David Elliott) writes:
< In article <1788@ttrdc.UUCP> levy@ttrdc.UUCP (Daniel R. Levy) writes:
< >In article <7180@mimsy.UUCP>, chris@mimsy.UUCP (Chris Torek) writes:
< >< And indeed, it does more:
< >< 	% egrep uucp:: /etc/passwd
< >< 	uucp::16:16:UNIX-to-UNIX Copy:/usr/spool/uucppublic:/usr/lib/uucp/recording
< >< 	% cat /usr/lib/uucp/recording
< >< 	#! /bin/awk NR > 1 { print }
< ><		[message] 
< >This is like using a cannon to kill a gopher.
< >Why not
< >
< >/bin/cat << !
< >	[message]
< >!
< >which will also work on systems other than "Berserkeley" UNIX.
< What? You mean that your /etc/password will allow you to put multiple
< lines in the shell field? What you suggest is that
< 	uucp::16:..:/bin/cat << !
< 		[message]
< is a valid entry in the password file.

No, no, that's not what I meant.  I meant to use a script containing that text.

< The point was that with #! you can use shell scripts or any other
< scripts as login shells or anywhere an executable program can go.

I looked at the source for /bin/login on a SVR2 machine (3B20).  It uses
execlp() to execute the login shell, so it can be a shell script.  (This
is probably a moot point anyhow since System V doesn't interpret "#!".)

< ...but you could not simply say
< 
< 	/bin/cat << !
< 		[message]
< 	!
< 
< and have it work unless login(1) executes the script vi sh.

I also tested a script containing just

/bin/cat << !
	[message]
!

as a "login shell" upon a real live BSD 4.2 machine.  Surprise, surprise,
it worked just dandy.  I also tried putting in a "ps -axww" and it showed the
script being executed by /bin/sh.  I tend to doubt that the machine I performed
this test upon is nonstandard in that respect.

< The fact that #!/bin/awk or #!/bin/sed or #!/usr/ucb/tail +2 will
< work is due to the generality of the #!, and generality is a big
< win.
< -- 
< David Elliott		{decvax,ucbvax,ihnp4}!decwrl!mips!dce

In some cases this IS nice.  But in the example given, it was still like using
a cannon to kill a gopher.
-- 
|------------dan levy------------|  Path: ..!{akgua,homxb,ihnp4,ltuxa,mvuxa,
|         an engihacker @        |		vax135}!ttrdc!ttrda!levy
|    at&t data systems division  |  Disclaimer:  try datclaimer.
|--------skokie, illinois--------|