GNU bug report logs - #44409
Example in manual no longer works

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

From: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
To: bug-gnu-emacs <at> gnu.org
Subject: Example in manual no longer works
Date: Tue, 03 Nov 2020 13:28:41 +0800

(info "(emacs) Grep Searching") Says

   For instance, you can chain ‘grep’ commands, like this: ...

But the example it then gives is for older emacs versions.

Newer emacs versions' grep string contains "--null" (proof: try
$ emacs -f grep
) which will cause the example to fail.

How can one rewrite the example to work with newer emacs versions?

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

From: Eli Zaretskii <eliz <at> gnu.org>
To: bug-gnu-emacs <at> gnu.org,
 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>,
 44409 <at> debbugs.gnu.org
Subject: Re: bug#44409: Example in manual no longer works
Date: Tue, 03 Nov 2020 09:16:58 +0200

On November 3, 2020 7:28:41 AM GMT+02:00, "積丹尼 Dan Jacobson" <jidanni <at> jidanni.org> wrote:
> (info "(emacs) Grep Searching") Says
> 
>    For instance, you can chain ‘grep’ commands, like this: ...
> 
> But the example it then gives is for older emacs versions.
> 
> Newer emacs versions' grep string contains "--null" (proof: try
> $ emacs -f grep
> ) which will cause the example to fail.
> 
> How can one rewrite the example to work with newer emacs versions?

I just tried the example in the manual with a recent version of Enacs, and the example works just fine.  So in what sense doesn't the example work for you?  And what is the significance of --null for this purpose?

IOW, I see no reason to rewrite the example.

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

From: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: bug-gnu-emacs <at> gnu.org, 44409 <at> debbugs.gnu.org
Subject: Re: bug#44409: Example in manual no longer works
Date: Tue, 03 Nov 2020 15:47:37 +0800

$ grep --color -nH --null -e a /etc/motd
/etc/motd:2:The programs included with the Debian GNU/Linux system are free software;
/etc/motd:3:the exact distribution terms for each program are described in the...
$ grep --color -nH --null -e a /etc/motd | grep x
Binary file (standard input) matches

>>>>> "EZ" == Eli Zaretskii <eliz <at> gnu.org> writes:
EZ> And what is the significance of --null for this purpose?

     grep -nH -e

is not the current emacs prompt. It is an older emacs prompt.

The current emacs prompt is

     grep --color -nH --null -e

You can verify this via
$ emacs -f grep

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

From: Eli Zaretskii <eliz <at> gnu.org>
To: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
Cc: bug-gnu-emacs <at> gnu.org, 44409 <at> debbugs.gnu.org
Subject: Re: bug#44409: Example in manual no longer works
Date: Tue, 03 Nov 2020 13:16:18 +0200

On November 3, 2020 9:47:37 AM GMT+02:00, "積丹尼 Dan Jacobson" <jidanni <at> jidanni.org> wrote:
> $ grep --color -nH --null -e a /etc/motd
> /etc/motd:2:The programs included with the Debian GNU/Linux system are
> free software;
> /etc/motd:3:the exact distribution terms for each program are
> described in the...
> $ grep --color -nH --null -e a /etc/motd | grep x
> Binary file (standard input) matches

The example in the manual doesn't mention /etc/motd of any other binary file.  It uses text files, where this issue doesn't exist.

If you are seeking information for how to use Grep with binary files, you should be looking in the Grep manual, not the Emacs manual.

> >>>>> "EZ" == Eli Zaretskii <eliz <at> gnu.org> writes:
> EZ> And what is the significance of --null for this purpose?
> 
>      grep -nH -e
> 
> is not the current emacs prompt. It is an older emacs prompt.
> 
> The current emacs prompt is
> 
>      grep --color -nH --null -e

Yes, but you need to edit that prompt anyway in order to type the command with a pipe, so the original prompt doesn't matter much.

I see no problem here that needs tk be fixed.

Message #26 received at submit <at> debbugs.gnu.org (full text, mbox):

From: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: bug-gnu-emacs <at> gnu.org, 44409 <at> debbugs.gnu.org
Subject: Re: bug#44409: Example in manual no longer works
Date: Wed, 04 Nov 2020 07:32:42 +0800

>>>>> "EZ" == Eli Zaretskii <eliz <at> gnu.org> writes:

EZ> The example in the manual doesn't mention /etc/motd of any other binary file.  It uses text files, where this issue doesn't exist.

Since when is /etc/motd a binary file?

If it were a binary file, the first grep,

>> $ grep --color -nH --null -e a /etc/motd
>> /etc/motd:2:The programs included with the Debian GNU/Linux system are free software;
>> /etc/motd:3:the exact distribution terms for each program are
>> described in the...

would fail.

But it doesn't. Only the second grep fails:

>> $ grep --color -nH --null -e a /etc/motd | grep x
>> Binary file (standard input) matches

So we see the issue indeed exists with text files!!

Double proof:

$ file /etc/motd
/etc/motd: ASCII text

Thus we see that one cannot simply slap

 "| grep bar | grep toto"

onto the end of a working grep command anymore!

Back when the manual was written, one could. But not anymore.

EZ> Yes, but you need to edit that prompt anyway in order to type the
EZ> command with a pipe, so the original prompt doesn't matter much.

No!

In the past one could simply slap the pipe(s) on to the back.

Now that no longer works.

Therefore the example needs to be rewritten to make it work again.

(Or specific instructions need to be given: "Be sure to remove any
'--null' that emacs has stuck in, for this example to work.")

Message #34 received at 44409-done <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
Cc: 44409-done <at> debbugs.gnu.org
Subject: Re: bug#44409: Example in manual no longer works
Date: Wed, 04 Nov 2020 05:24:40 +0200

> From: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
> Cc: bug-gnu-emacs <at> gnu.org, 44409 <at> debbugs.gnu.org
> Date: Wed, 04 Nov 2020 07:32:42 +0800
> 
> >>>>> "EZ" == Eli Zaretskii <eliz <at> gnu.org> writes:
> 
> EZ> The example in the manual doesn't mention /etc/motd of any other binary file.  It uses text files, where this issue doesn't exist.
> 
> Since when is /etc/motd a binary file?

I didn't say it was.

> >> $ grep --color -nH --null -e a /etc/motd | grep x
> >> Binary file (standard input) matches
> 
> So we see the issue indeed exists with text files!!

No, it exists if you use Grep incorrectly.

> EZ> Yes, but you need to edit that prompt anyway in order to type the
> EZ> command with a pipe, so the original prompt doesn't matter much.
> 
> No!
> 
> In the past one could simply slap the pipe(s) on to the back.
> 
> Now that no longer works.
> 
> Therefore the example needs to be rewritten to make it work again.

The example already works without any changes, so it doesn't need to
be rewritten.

> (Or specific instructions need to be given: "Be sure to remove any
> '--null' that emacs has stuck in, for this example to work.")

That's the stuff for Grep manual, not for Emacs.

So I don't see any problem here to fix, and I'm closing this bug
report.

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