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Re: what is the regular expression that matches nothing? -- I think it i
From: |
Randy Yates |
Subject: |
Re: what is the regular expression that matches nothing? -- I think it is the null expression. When I do "egrep '' somefile" the result is the same as when I do "cat somefile". The result of "egrep -v '' somefile" is, as expected, nothing. HTH |
Date: |
Fri, 24 Dec 2004 17:40:52 GMT |
User-agent: |
Gnus/5.1002 (Gnus v5.10.2) XEmacs/21.4 (Rational FORTRAN, windows-nt) |
Stan Brown <the_stan_brown@fastmail.fm> writes:
> There is no regular expression that matches nothing.
>
> I you want to match a zero-length line, use
> ^$
>
> But the idea of matching nothing has an inherent contradiction.
I don't see that. Can you explain why you say this?
> Why don't you tell us what you're actually trying to accomplish?
Sure, Stan. I'm trying to setup the EFS package in XEmacs to use a
gateway for FTP. In this mode, EFS requires a regular expression to
identify which machines are accessible without having to go through
the gateway. In my case (this is at work where we have a firewall)
that would be "no machine," i.e., all machines I FTP to (with XEmacs)
will be outside the firewall. Thus the regexp has to match "nothing."
--
% Randy Yates % "Rollin' and riding and slippin' and
%% Fuquay-Varina, NC % sliding, it's magic."
%%% 919-577-9882 %
%%%% <yates@ieee.org> % 'Living' Thing', *A New World Record*, ELO
http://home.earthlink.net/~yatescr
- what is the regular expression that matches nothing?, Randy Yates, 2004/12/23
- Re: what is the regular expression that matches nothing? -- I think it is the null expression. When I do "egrep '' somefile" the result is the same as when I do "cat somefile". The result of "egrep -v '' somefile" is, as expected, nothing. HTH, me, 2004/12/23
- Re: what is the regular expression that matches nothing? -- I think it is the null expression. When I do "egrep '' somefile" the result is the same as when I do "cat somefile". The result of "egrep -v '' somefile" is, as expected, nothing. HTH, Randy Yates, 2004/12/23
- Re: what is the regular expression that matches nothing?, me, 2004/12/23
- Re: what is the regular expression that matches nothing? -- I think it is the null expression. When I do "egrep '' somefile" the result is the same as when I do "cat somefile". The result of "egrep -v '' somefile" is, as expected, nothing. HTH, Stan Brown, 2004/12/23
- Re: what is the regular expression that matches nothing? -- I think it is the null expression. When I do "egrep '' somefile" the result is the same as when I do "cat somefile". The result of "egrep -v '' somefile" is, as expected, nothing. HTH,
Randy Yates <=
- Re: what is the regular expression that matches nothing? -- I think it is the null expression. When I do "egrep '' somefile" the result is the same as when I do "cat somefile". The result of "egrep -v '' somefile" is, as expected, nothing. HTH, Andrei Voropaev, 2004/12/27
Re: what is the regular expression that matches nothing?, Paul Jarc, 2004/12/27