Path: utzoo!yunexus!oz
From: oz@yunexus.UUCP (Ozan Yigit)
Newsgroups: comp.unix.wizards
Subject: Re: what should egrep '|root' /etc/passwd print? (Everything)
Keywords: regular-expressions, egrep, gnu-egrep
Message-ID: <855@yunexus.UUCP>
Date: 15 Sep 88 14:59:07 GMT
Article-I.D.: yunexus.855
References: <44414@beno.seismo.CSS.GOV> <8492@smoke.ARPA>
Reply-To: oz@yunexus.UUCP (Ozan Yigit)
Organization: York U. C. S. Impressive-Sounding-Name Labs.
Lines: 32

In article <8492@smoke.ARPA> Doug Gwyn  writes:
>In article <44414@beno.seismo.CSS.GOV> Rick Adams writes:
>>What should 
>>	egrep '|root' /etc/passwd
>>print?
>
>The question of how to handle empty strings in regular expressions
>does not have a clear-cut answer.  

Oh ??? Just what does '(foo)?' match on your egrep ?? It just happens
to be the same thing as E|foo (E for Epsilon, or the null match),
or exactly what rick wants to match. It had a clear cut answer before,
but I am sure it is lost somewhere along the line. 

> .."sam", which has the most powerful
>regular expression mechanism of any of the editor-like programs I use,
>says the following:
>	?no operand for `|'

A parsing glitch no doubt. See, some expressions are more regular :-)
then others, so "sam" will no doubt accept the expression under a
disguise of "(foo)?". 

In any case, Rick should probably use jaw-improved-gnu-egrep for
correct results.

oz
-- 
Crud that is not paged	        | Usenet: ...!utzoo!yunexus!oz
is still crud. 			|   ...uunet!mnetor!yunexus!oz
	andrew@alice		| Bitnet: oz@[yulibra|yuyetti]
				| Phonet: +1 416 736-5257x3976