How to avoid /dev/null at the end of grep-command

How to avoid /dev/null at the end of grep-command

[al.coyote]

Hello,

When running M-x grep, emacs adds a /dev/null after the list of files.
That's a secure idea most of the times, but when running complex grep
command, this is annoying. For example something like:

grep -n -A2 my_function  *  |  grep -n '\n'

won't work, as emacs will transform this command as

grep -n -A2 my_function  *  |  grep -n '\n' /dev/null

I can add /dev/stdin to the second grep, but the file name will be
garbaged too.

Setting a default grep command does not solve the problem.

Any solution to avoid the /dev/null, without modifying compile.el ?

Thanks in advance.

Al

Re: How to avoid /dev/null at the end of grep-command

[Eli Zaretskii]

> From: al.coyote@gmail.com
> Date: 2 Mar 2007 01:20:35 -0800
> 
> Any solution to avoid the /dev/null, without modifying compile.el ?

I'm guessing that this is Emacs 21.x; if not, holler.  (I shouldn't be
guessing, btw: please always state your Emacs version and the OS.)

One way to work around this is to write a wrapper command that binds
null-device to nil and then invokes the original `grep' command.  You
can put this command in your .emacs.

Re: How to avoid /dev/null at the end of grep-command

[al.coyote]

Hello Eli,

On 2 mar, 14:49, Eli Zaretskii <e...@gnu.org> wrote:
> > From: al.coy...@gmail.com
> > Date: 2 Mar 2007 01:20:35 -0800
>
> > Any solution to avoid the /dev/null, without modifying compile.el ?
>
> I'm guessing that this is Emacs 21.x; if not, holler.  (I shouldn't be
> guessing, btw: please always state your Emacs version and the OS.)
>
> One way to work around this is to write a wrapper command that binds
> null-device to nil and then invokes the original `grep' command.  You
> can put this command in your .emacs.

I'm using emacs 21 on linux, but as this feature comes from compile.el
the behaviour should be the same on most architectures.
This behaviour is very old, maybe version 20 and even 19 did have it
(sorry I don't have these versions handy).

Thanks for your suggestion, I have found another one. Just end your
complex command with cat -, this command will do nothing except
protect from the /dev/null
So M-x grep with grep -n -A2 printf * | grep '\\n' | sed -e s/-/:/g |
cat -
will be transformed by emacs into
grep -n -A2 printf * | grep '\\n' | sed -e s/-/:/g | cat - /dev/null
which will do the job.

Al

Re: How to avoid /dev/null at the end of grep-command

[Eli Zaretskii]

> From: al.coyote@gmail.com
> Date: 3 Mar 2007 00:09:46 -0800
> >
> > I'm guessing that this is Emacs 21.x; if not, holler.  (I shouldn't be
> > guessing, btw: please always state your Emacs version and the OS.)
> 
> I'm using emacs 21 on linux, but as this feature comes from compile.el
> the behaviour should be the same on most architectures.

You see, the problem is, I use the development version of Emacs (which
will shortly become Emacs 22.1), where there are other solutions.
Many Emacs users use this development version as well.  That is why
version information is important.

> Thanks for your suggestion, I have found another one.

Glad you solved this.