GNU bug report logs - #78891
Option to make grep always exit with 0

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

From: Thomas Güttler Mailinglisten <guettliml <at> gmail.com>
To: bug-grep <at> gnu.org
Subject: Option to make grep always exit with 0
Date: Tue, 24 Jun 2025 11:49:21 +0200

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

Hi,

after trying several tools like SaltStack and Ansible and several CI tools,
I came
to the conclusion that a Bash script is often the most convenient and
powerful solution.

To make Bash more robust, I use the "strict mode".

This works fine, except that very often I want to filter out some output,
and it
does not matter to me if there is a match or not.

Afaik there is no option to make `grep` always exit with a zero exit
status. No matter if a match was found or not. Errors like "file not found"
should still return a non-zero exit status.

Just out of curiosity, would you accept a patch to implement that?

Which command line argument could be used for that option?

Regard,
  Thomas Güttler

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Message #8 received at 78891 <at> debbugs.gnu.org (full text, mbox):

From: "Dale R. Worley" <Dale.Worley <at> comcast.net>
To: Thomas Güttler Mailinglisten <guettliml <at> gmail.com>
Cc: 78891 <at> debbugs.gnu.org
Subject: Re: bug#78891: Option to make grep always exit with 0
Date: Tue, 24 Jun 2025 14:22:28 -0400

Thomas Güttler Mailinglisten <guettliml <at> gmail.com> writes:
> To make Bash more robust, I use the "strict mode".
>
> This works fine, except that very often I want to filter out some
> output, and it does not matter to me if there is a match or not.
>
> Afaik there is no option to make `grep` always exit with a zero exit
> status. No matter if a match was found or not. Errors like "file not found"
> should still return a non-zero exit status.

Well, this isn't what you asked for, but it's a reasonaby terse way to
get the effect without modifying grep:

    grep ... || [[ $? != 2 ]]

That has an exit status of 1 if grep exits with 2, and an exit status of
0 otherwise.

Dale

Message #11 received at 78891 <at> debbugs.gnu.org (full text, mbox):

From: Thomas Güttler Mailinglisten <guettliml <at> gmail.com>
Cc: 78891 <at> debbugs.gnu.org
Subject: Re: bug#78891: Option to make grep always exit with 0
Date: Wed, 25 Jun 2025 07:28:49 +0200

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

Hi Dale, thank you for your reply. Currently, I work around like this:

echo -e "foo\nbar" | { grep '^#' >comments.txt || true; } |
some-other-command

Related: My Bash Strict Mode. Handle non-zero exit codes
<https://github.com/guettli/bash-strict-mode/blob/main/README.md#bash-strict-mode-handle-non-zero-exit-codes>

This works, but it is not nice to read and more typing.

There are many ways to work around that. During the last months I wrote
a lot of Bash code, and often I needed to handle the non-zero exit code of
grep.

It would be handy to have an option to make grep always return zero (except
"file not found" or similar errors).

Why not?

Before creating a patch, I would like to know which command line option you
prefer.

There are not many characters left, which could be used.

What about `-g` like "good, even if nothing was found"?

Or `-t` like always return true (zero exit status).

But first: Would a patch be acceptable?

Regards,
  Thomas



Am Di., 24. Juni 2025 um 20:22 Uhr schrieb Dale R. Worley <
Dale.Worley <at> comcast.net>:

> Thomas Güttler Mailinglisten <guettliml <at> gmail.com> writes:
> > To make Bash more robust, I use the "strict mode".
> >
> > This works fine, except that very often I want to filter out some
> > output, and it does not matter to me if there is a match or not.
> >
> > Afaik there is no option to make `grep` always exit with a zero exit
> > status. No matter if a match was found or not. Errors like "file not
> found"
> > should still return a non-zero exit status.
>
> Well, this isn't what you asked for, but it's a reasonaby terse way to
> get the effect without modifying grep:
>
>     grep ... || [[ $? != 2 ]]
>
> That has an exit status of 1 if grep exits with 2, and an exit status of
> 0 otherwise.
>
> Dale
>

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Message #14 received at 78891 <at> debbugs.gnu.org (full text, mbox):

From: Martin Schulte <gnu <at> schrader-schulte.de>
To: Thomas Güttler Mailinglisten <guettliml <at> gmail.com>
Cc: 78891 <at> debbugs.gnu.org
Subject: Re: bug#78891: Option to make grep always exit with 0
Date: Wed, 25 Jun 2025 08:09:43 +0200

Hello Thomas!

> echo -e "foo\nbar" | { grep '^#' >comments.txt || true; } |
> some-other-command
> 
> Related: My Bash Strict Mode. Handle non-zero exit codes
> <https://github.com/guettli/bash-strict-mode/blob/main/README.md#bash-strict-mode-handle-non-zero-exit-codes>
> 
> This works, but it is not nice to read and more typing.

What about a

grep_always_true() {
  grep "$@" || true
}

?

Best regards,

Martin

Message #17 received at 78891 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Thomas Güttler Mailinglisten <guettliml <at> gmail.com>
Cc: 78891 <at> debbugs.gnu.org
Subject: Re: bug#78891: Option to make grep always exit with 0
Date: Wed, 25 Jun 2025 10:14:52 -0700

On 2025-06-24 22:28, Thomas Güttler Mailinglisten wrote:
>   During the last months I wrote
> a lot of Bash code, and often I needed to handle the non-zero exit code of
> grep.
> 
> It would be handy to have an option to make grep always return zero (except
> "file not found" or similar errors).

I dunno, there are several commands like grep that return exit status 
1/2 for different kinds of "failure". ("diff", for example.) I doubt 
whether we want to add such an option to all these commands.

"grep GREPARGS || test $? = 1" is short and easy to remember and has 
worked everywhere for decades. If you dislike its syntax you can package 
it inside a shell function.

Message #20 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Dennis Clarke <dclarke <at> blastwave.org>
To: bug-grep <at> gnu.org
Subject: Re: bug#78891: Option to make grep always exit with 0
Date: Wed, 25 Jun 2025 13:51:15 -0400

On 6/25/25 13:14, Paul Eggert wrote:
> On 2025-06-24 22:28, Thomas Güttler Mailinglisten wrote:
>>   During the last months I wrote
>> a lot of Bash code, and often I needed to handle the non-zero exit 
>> code of
>> grep.
>>
>> It would be handy to have an option to make grep always return zero 
>> (except
>> "file not found" or similar errors).
> 
> I dunno, there are several commands like grep that return exit status 
> 1/2 for different kinds of "failure". ("diff", for example.) I doubt 
> whether we want to add such an option to all these commands.
> 
> "grep GREPARGS || test $? = 1" is short and easy to remember and has 
> worked everywhere for decades. If you dislike its syntax you can package 
> it inside a shell function.
> 
> 

I am at great risk of falling into a bike shed[1] here. If grep
works fine and all is happy then we get a zero return value. All
other possible situations *should* return a non-zero error status
that helps silly old UNIX people like me.

If someone needs to write if-then-else-what? clause stuff in code
then that is correct behavior. Why fix that which works fine?

-- 
--
Dennis Clarke
RISC-V/SPARC/PPC/ARM/CISC
UNIX and Linux spoken

[1] https://en.wikipedia.org/wiki/Law_of_triviality

Message #23 received at 78891 <at> debbugs.gnu.org (full text, mbox):

From: "Dale R. Worley" <Dale.Worley <at> comcast.net>
To: Thomas Güttler Mailinglisten <guettliml <at> gmail.com>
Cc: 78891 <at> debbugs.gnu.org
Subject: Re: bug#78891: Option to make grep always exit with 0
Date: Wed, 25 Jun 2025 20:49:49 -0400

Thomas Güttler Mailinglisten <guettliml <at> gmail.com> writes:
> Hi Dale, thank you for your reply. Currently, I work around like this:
>
> echo -e "foo\nbar" | { grep '^#' >comments.txt || true; } |
> some-other-command

The difficulty with that code is that it doesn't satisfy the requirement
you stated:

> Afaik there is no option to make `grep` always exit with a zero exit
> status. No matter if a match was found or not. Errors like "file not found"
> should still return a non-zero exit status.

That's why you need the test "$? != 2".

Dale

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