bug#63819: closed (Gnu `grep '.*'` does not match an empty string.)

[GNU bug Tracking System]

Your message dated Wed, 31 May 2023 20:15:30 -0700
with message-id <9f737863-fbad-b673-930d-e5ccca682266@cs.ucla.edu>
and subject line Re: bug#63819: Gnu `grep '.*'` does not match an empty string.
has caused the debbugs.gnu.org bug report #63819,
regarding Gnu `grep '.*'` does not match an empty string.
to be marked as done.

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63819: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=63819
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--- Begin Message --- Subject: Gnu `grep '.*'` does not match an empty string. Date: Wed, 31 May 2023 17:18:30 +0000

I discovered only today that the following commands all behave identically:

• grep -q '.*'
• grep -q '.\+'
• grep -q .
• grep -qE '.*'
• grep -qE '.+'
• grep -qE .
  

Gnu grep documentation says:

The period ‘.’ matches any single character. It is unspecified whether ‘.’ matches an encoding error.

and

‘*’

The preceding item is matched zero or more times.

I would think that an empty string matches "zero or more of any single character".

Can anyone point out where the documentation says otherwise?

Bob Vincent (US) 

PwC IT - NGC - PUPPET DEV OPS | Senior Manager

Work: 906-984-3549
Mobile: 770-744-1792
PricewaterhouseCoopers LLP
@workday @github @ServiceNow

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--- End Message ---

> --- Begin Message ---
>
>
>
> Subject: 
>
> Re: bug#63819: Gnu `grep '.*'` does not match an empty string.
>
>
>
>
> Date: 
>
> Wed, 31 May 2023 20:15:30 -0700
>
>
>
>
> User-agent: 
>
> Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.11.0
>
>
>
>
> On 2023-05-31 19:17, Bob Vincent Il (US) wrote:
> > Okay, but `echo ''` does not output an empty string. It outputs a line feed 
> > character.
>
> The line feed is not considered. Grep looks only for matches of "any 
> part of the line excluding the terminating <newline>" 
> <https://pubs.opengroup.org/onlinepubs/9699919799/utilities/grep.html>.
>
> Closing the bug report as it appears to be due to a misunderstanding of 
> how 'grep' works.
>
>
> --- End Message ---