grep < fifo fails

grep < fifo fails

[Ole Tange]

This works:

$ mkfifo fifo
$ echo > fifo & grep .  fifo
[1] 10232
[1]+  Done                    echo > fifo

But this fails:

$ echo > fifo & grep . < fifo
[1] 11756
grep: (standard input): Invalid argument
[1]+  Done                    echo > fifo

I see the same behavior on MINGW, but I do not see the same behavior on GNU/Linux.


Regards,

Ole Tange


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Re: grep < fifo fails

[Marco Atzeri]

Am 03.10.2018 um 17:37 schrieb Ole Tange:
> This works:
>
> $ mkfifo fifo
> $ echo > fifo & grep .  fifo
> [1] 10232
> [1]+  Done                    echo > fifo
>
> But this fails:
>
> $ echo > fifo & grep . < fifo
> [1] 11756
> grep: (standard input): Invalid argument
> [1]+  Done                    echo > fifo
>
> I see the same behavior on MINGW, but I do not see the same behavior on GNU/Linux.
>
>
> Regards,
>
> Ole Tange

I assume it is a consequence of the same problem on files.
You can not use the same source for input and output.

$ echo "prova" > prova.txt

$ cat prova.txt
prova

$ cat prova.txt > prova.txt

$ cat prova.txt

the file was erased



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Re: grep < fifo fails

[Houder]

On Wed, 3 Oct 2018 15:37:14, Ole Tange wrote:
> This works:
> 
> $ mkfifo fifo
> $ echo > fifo & grep .  fifo
> [1] 10232
> [1]+  Done                    echo > fifo
> 
> But this fails:
> 
> $ echo > fifo & grep . < fifo
> [1] 11756
> grep: (standard input): Invalid argument
> [1]+  Done                    echo > fifo
> 
> I see the same behavior on MINGW, but I do not see the same behavior on GNU=
> /Linux.

64-@@ bash --version
GNU bash, version 4.4.12(3)-release (x86_64-unknown-cygwin)64
..
64-@@ echo > fifo & grep . < fifo
[1] 1192
[1]+  Done                    echo > fifo
64-@@ grep --version
grep (GNU grep) 3.0
Packaged by Cygwin (3.0-2)
..
Written by Mike Haertel and others, see <http://git.sv.gnu.org/cgit/grep.git/tree/AUTHORS>.
64-@@ file fifo
fifo: very short file (no magic)
64-@@

@@ bash --version
GNU bash, version 4.4.12(3)-release (i686-pc-cygwin)
..
@@ echo > fifo & grep . < fifo
[1] 4852
[1]+  Done                    echo > fifo
@@ grep --version
grep (GNU grep) 3.0
Packaged by Cygwin (3.0-2)
..
Written by Mike Haertel and others, see <http://git.sv.gnu.org/cgit/grep.git/tree/AUTHORS>.
@@ file fifo
fifo: very short file (no magic)
@@

Your version of grep ?????

Regards,
Henri


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Re: grep < fifo fails

[Houder]

On Wed, 03 Oct 2018 20:46:11, Houder wrote:
> On Wed, 3 Oct 2018 15:37:14, Ole Tange wrote:
> > This works:
> > 
> > $ mkfifo fifo
> > $ echo > fifo & grep .  fifo
> > [1] 10232
> > [1]+  Done                    echo > fifo
> > 
> > But this fails:
> > 
> > $ echo > fifo & grep . < fifo
> > [1] 11756
> > grep: (standard input): Invalid argument
> > [1]+  Done                    echo > fifo
> > 
> > I see the same behavior on MINGW, but I do not see the same behavior on GNU=
> > /Linux.

My apologies. Did not read you post as careful as I should have the first time.
You are correct: grep is in error here.

(utilities from e.g. coreutils do not show this error in the context above)

Regards,
Henri


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Re: grep < fifo fails

[Houder]

On Thu, 04 Oct 2018 18:02:03, Houder wrote:
> On Wed, 03 Oct 2018 20:46:11, Houder wrote:
> > On Wed, 3 Oct 2018 15:37:14, Ole Tange wrote:
> > > This works:
> > > 
> > > $ mkfifo fifo
> > > $ echo > fifo & grep .  fifo
> > > [1] 10232
> > > [1]+  Done                    echo > fifo
> > > 
> > > But this fails:
> > > 
> > > $ echo > fifo & grep . < fifo
> > > [1] 11756
> > > grep: (standard input): Invalid argument
> > > [1]+  Done                    echo > fifo
> > > 
> > > I see the same behavior on MINGW, but I do not see the same behavior on GNU=
> > > /Linux.
> 
> My apologies. Did not read your post as careful as I should have the first time.
> You are correct: grep is in error here.

Filed this bug at bug-grep@gnu.org; it is filed under number 32943.

 - https://debbugs.gnu.org/cgi/bugreport.cgi?bug=32943

Regards,
Henri


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Re: grep < fifo fails

[Houder]

On Fri, 05 Oct 2018 17:32:16, Houder wrote:
> On Thu, 04 Oct 2018 18:02:03, Houder wrote:
> > On Wed, 03 Oct 2018 20:46:11, Houder wrote:
> > > On Wed, 3 Oct 2018 15:37:14, Ole Tange wrote:
> > > > This works:
> > > > 
> > > > $ mkfifo fifo
> > > > $ echo > fifo & grep .  fifo
> > > > [1] 10232
> > > > [1]+  Done                    echo > fifo
> > > > 
> > > > But this fails:
> > > > 
> > > > $ echo > fifo & grep . < fifo
> > > > [1] 11756
> > > > grep: (standard input): Invalid argument
> > > > [1]+  Done                    echo > fifo
> > > > 
> > > > I see the same behavior on MINGW, but I do not see the same behavior on GNU=
> > > > /Linux.
> > 
> > My apologies. Did not read your post as careful as I should have the first time.
> > You are correct: grep is in error here.
> 
> Filed this bug at bug-grep@gnu.org; it is filed under number 32943.
> 
>  - https://debbugs.gnu.org/cgi/bugreport.cgi?bug=32943
> 

grep fails on Cygwin because lseek() on Cygwin fails to recognize
that it is applied to a FIFO. As result of that, it returns EINVAL
in errno, where it should return ESPIPE.

Receiving the wrong value in errno forces reset() (in src/grep.c)
to return false, upon which grep fails.

Before v2.27 of grep, a call to S_ISREG(st->st_mode) in reset()
prevented the call of lseek() and made reset() return true.

The call to S_ISREG() has been removed in v2.27 of grep.

The solution would be either to correct Cygwin's executive or to
insert a Cygwin-specific kludge in grep (in reset() ).

Regards,
Henri


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Re: grep < fifo fails

[Eric Blake]

On 10/8/18 3:24 AM, Houder wrote:
> grep fails on Cygwin because lseek() on Cygwin fails to recognize
> that it is applied to a FIFO. As result of that, it returns EINVAL
> in errno, where it should return ESPIPE.
> 
> Receiving the wrong value in errno forces reset() (in src/grep.c)
> to return false, upon which grep fails.
> 
> Before v2.27 of grep, a call to S_ISREG(st->st_mode) in reset()
> prevented the call of lseek() and made reset() return true.
> 
> The call to S_ISREG() has been removed in v2.27 of grep.
> 
> The solution would be either to correct Cygwin's executive or to

s/executive/dll/

> insert a Cygwin-specific kludge in grep (in reset() ).

I see no reason to do a one-off kludge to my build of grep (since that 
does not scale - every other app that also makes decisions based on 
errno values would have to make the same kludge), compared to just 
fixing cygwin1.dll for everyone.

But thanks for isolating the problem!

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Re: grep < fifo fails

[Corinna Vinschen]

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On Oct  8 10:03, Eric Blake wrote:
> On 10/8/18 3:24 AM, Houder wrote:
> > grep fails on Cygwin because lseek() on Cygwin fails to recognize
> > that it is applied to a FIFO. As result of that, it returns EINVAL
> > in errno, where it should return ESPIPE.
> > 
> > Receiving the wrong value in errno forces reset() (in src/grep.c)
> > to return false, upon which grep fails.
> > 
> > Before v2.27 of grep, a call to S_ISREG(st->st_mode) in reset()
> > prevented the call of lseek() and made reset() return true.
> > 
> > The call to S_ISREG() has been removed in v2.27 of grep.
> > 
> > The solution would be either to correct Cygwin's executive or to
> 
> s/executive/dll/
> 
> > insert a Cygwin-specific kludge in grep (in reset() ).
> 
> I see no reason to do a one-off kludge to my build of grep (since that does
> not scale - every other app that also makes decisions based on errno values
> would have to make the same kludge), compared to just fixing cygwin1.dll for
> everyone.
> 
> But thanks for isolating the problem!

I pushed a patch.  Thanks for tracking this down, Henri!


Corinna

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Red Hat

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Re: grep < fifo fails

[Houder]

On Mon, 08 Oct 2018 10:24:01, Houder wrote:
...

> > > > On Wed, 3 Oct 2018 15:37:14, Ole Tange wrote:
> > > > > This works:
> > > > > 
> > > > > $ mkfifo fifo
> > > > > $ echo > fifo & grep .  fifo
> > > > > [1] 10232
> > > > > [1]+  Done                    echo > fifo
> > > > > 
> > > > > But this fails:
> > > > > 
> > > > > $ echo > fifo & grep . < fifo
> > > > > [1] 11756
> > > > > grep: (standard input): Invalid argument
> > > > > [1]+  Done                    echo > fifo
...

> grep fails on Cygwin because lseek() on Cygwin fails to recognize
> that it is applied to a FIFO. As result of that, it returns EINVAL
> in errno, where it should return ESPIPE.
[snip]

> The solution would be either to correct Cygwin's executive or to
> insert a Cygwin-specific kludge in grep (in reset() ).

Right.

64-@@ echo aaa > fifo & grep . < fifo
[1] 3956
aaa
[2]+  Done                    echo aaa > fifo

The following rough patch to the Cygwin executive ... uhm, Cygwin DLL,
makes the above work.

winsup/cygwin/fhandler.h:

class fhandler_fifo: public fhandler_base_overlapped
{
...
// Henri
  off_t lseek (off_t, int)
  {
    set_errno (ESPIPE);
    return -1;
  }
...
};

(I cheated; I did a copy/paste of what is already present in fhandler.h)

Regards,
Henri


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