Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ames!nrl-cmf!cmcl2!rutgers!bellcore!faline!thumper!ulysses!andante!alice!andrew
From: andrew@alice.UUCP (Andrew Hume)
Newsgroups: comp.unix.wizards
Subject: Re: what should egrep '|root' /etc/passwd print?
Summary: why it is.
Message-ID: <8202@alice.UUCP>
Date: 15 Sep 88 05:47:28 GMT
References: <44414@beno.seismo.CSS.GOV> <68203@sun.uucp>
Organization: AT&T Bell Laboratories, Murray Hill NJ
Lines: 15



it is true that youhave to think carefully about null regular expressions.
i (and gre) believe as sam does, '|root' is a syntax error as | is dyadic.
the behaviour of matching every line is just wrong. egrep handles this
as a special case; recall that egrep takes \n as a synonym for |.
aho wanted to forgive the user for being sloppy with quotes and blank lines
as in egrep '
abc
def
' file

which ordinarily has superfluous \n at the beginning and end. i agree that this
is a flimsy aim but that is the current practice with egrep.
i think that it is clear that grep '' file is always a syntax error;
there is no useful interpretation of such a regular expression.