GNU bug report logs - #20443
grep pattern is forward slash + star

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Clay Hansen <clayh <at> ayre.com>
To: bug-grep <at> gnu.org
Subject: grep pattern is forward slash + star
Date: Mon, 27 Apr 2015 13:05:11 -0600

Dear Coders,

if I echo 'a  *  z' | grep '/*' it succeeds and prints 'a  *  z'.
Can this be right?

echo 'a  *  z' | grep -F '/*' fails as expected.

Tested in Salix on grep-2.14 and freshly compiled grep-2.21.

Thanks,

Message #12 received at 20443-done <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: Clay Hansen <clayh <at> ayre.com>, 20443-done <at> debbugs.gnu.org
Cc: GNU bug tracker automated control server <control <at> debbugs.gnu.org>
Subject: Re: bug#20443: grep pattern is forward slash + star
Date: Mon, 27 Apr 2015 14:53:02 -0600

[Message part 1 (text/plain, inline)]

tag 20443 notabug
thanks

On 04/27/2015 01:05 PM, Clay Hansen wrote:
> Dear Coders,
> 
> if I echo 'a  *  z' | grep '/*' it succeeds and prints 'a  *  z'.
> Can this be right?

Yes.  The regular expression '/*' says to match 0-or-more instances of
'/'. 'a  *  z' has zero instances of '/', so it matches and gets printed.

> 
> echo 'a  *  z' | grep -F '/*' fails as expected.

That's the literal pattern '/*', which does not appear in your input.

Remember, to convert the literal pattern of '/*' under -F to a regular
expression when not using -F, you must escape any characters that are
otherwise special to regular expressions.  Your second command would be
equivalent to:

echo 'a  *  z' | grep '/\*'

where the '*' now matches a literal star rather than being the
0-or-more-operator.

As such, this is not a bug, so I'm closing the report.  However, feel
free to ask further questions on the topic.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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