Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!usc!srhqla!quad1!ttidca!paulb
From: paulb@ttidca.TTI.COM (Paul Blumstein)
Newsgroups: comp.unix.questions
Subject: Re: Another sed question.
Message-ID: <8249@ttidca.TTI.COM>
Date: 6 Dec 89 21:49:55 GMT
References: <37091@ames.arc.nasa.gov> <4694@pinas.cs.vu.nl> <1989Dec5.112101.15906@gdt.bath.ac.uk>
Reply-To: paulb@ncc1701.tti.com (Paul Blumstein)
Organization: DAM: Mothers Against Dyslexia
Lines: 29

In article <1989Dec5.112101.15906@gdt.bath.ac.uk> exspes@gdr.bath.ac.uk (P E Smee) writes:
+In article <4694@pinas.cs.vu.nl> maart@cs.vu.nl (Maarten Litmaath) writes:
+>Probably:
+>
+>	#!/bin/sed 1d
+>	<the rest of the script>
+>
+>When you try to execute this script, the kernel opens it to find out what kind
+>of executable it is.  The header of a *binary* includes the size of the text,
+>data and bss segments etc..  This file, however, isn't a binary: it's an
+>EXECUTABLE shell script.  The kernel discovers the `#!' MAGIC NUMBER and takes
+>the following word as the real executable to start.  There may be 1 option
+
+Question is, is this #! trick actually documented anywhere?  I certainly can't
+find it in any obvious place in my FM's (mostly sysV and 4.2bsd).  If so,
+where?  Is it a 4.3bsd feature, or something?  (I see a quick 'mention in
+passing' in J.E.Lapin's 'Portable C and Unix System Programming', which
+seems to imply that it isn't -- portable, that is.)

Yes!  The documentation is hidden.  It is magic, isn't it?  While it is
tempting to say that a magician doesn't reveal secrets, I'll tell you if
you promise not to tell anyone else :-).  The man page for execve (section
2) is where to look.
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