openssh unix dev - May 2020 - [PATCH] Use POSIX standardized options for head(1) and tail(1)

---
 Makefile.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile.in b/Makefile.in
index 304d96cd..47e04c02 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -353,7 +353,7 @@ depend-rebuild:
 	rm -f config.h
 	touch config.h
 	makedepend -w1000 -Y. -f .depend *.c 2>/dev/null
-	(head -2 .depend; tail +3 .depend | sort) >.depend.tmp
+	(head -n 2 .depend; tail -n +3 .depend | sort) >.depend.tmp
 	mv .depend.tmp .depend
 	rm -f config.h
 
-- 
2.26.2

Hi Michael,

Using POSIX command-line semantics is a fine goal. Someone might drop
the backward-compatiblity of the commands and then things would begin to
break. However, there is an alternative. Do not use these POSIX commands
that have changed their command-line syntax if one that exists and is
more stable is also available.
> @@ -353,7 +353,7 @@ depend-rebuild:
>         rm -f config.h
>         touch config.h
>         makedepend -w1000 -Y. -f .depend *.c 2>/dev/null
> -       (head -2 .depend; tail +3 .depend | sort) >.depend.tmp
> +       (head -n 2 .depend; tail -n +3 .depend | sort) >.depend.tmp
>         mv .depend.tmp .depend
>         rm -f config.h
I am speaking of the use of 'sed' which has been pretty stable since at
least 1992 and mostly the same going back to 1974.

Using sed for compatibility with all possible portable releases seems
'better' to me than just upgrading a command because POSIX thinks it is
a good idea.

For example:

   head -2 == head -n 2 == sed 'n;q'

   tail +3 == tail -n +3 == sed '1,2d'

The sed program has been around a lot longer without these command-line
semantics changing for POSIX. 

These idioms should work fine going back to at least the BSD version of
sed from 1992 by Diomidis Spinellis and maybe even going back to Lee E.
McMahon's version in 1974.

@@ -353,7 +353,7 @@ depend-rebuild:
        rm -f config.h
        touch config.h
        makedepend -w1000 -Y. -f .depend *.c 2>/dev/null
-       (head -2 .depend; tail +3 .depend | sort) >.depend.tmp
+       (sed 'n;q' .depend; sed '1,2d' .depend | sort)
>.depend.tmp
        mv .depend.tmp .depend
        rm -f config.h

The idea of the OpenSSH portable release is to be portable across a LOT
of UNIX (and even some non-UNIX releases). If that is the goal, why
enforce the need to fetch and build POSIX-compliant versions of head and
tail for very old systems?

	Be safe, stay healthy,
	-- Mark

On 2020-04-25, Mark D. Baushke <mdb at juniper.net>
wrote:
> Hi Michael,
Hi Mark,
> Using POSIX command-line semantics is a fine goal. Someone might drop
> the backward-compatiblity of the commands and then things would begin to
> break.
Indeed, that's what motivated the patch. The version of tail on my
system does not support the legacy options.
> However, there is an alternative. Do not use these POSIX commands
> that have changed their command-line syntax if one that exists and is
> more stable is also available.
>
>> @@ -353,7 +353,7 @@ depend-rebuild:
>>         rm -f config.h
>>         touch config.h
>>         makedepend -w1000 -Y. -f .depend *.c 2>/dev/null
>> -       (head -2 .depend; tail +3 .depend | sort) >.depend.tmp
>> +       (head -n 2 .depend; tail -n +3 .depend | sort) >.depend.tmp
>>         mv .depend.tmp .depend
>>         rm -f config.h
>
> I am speaking of the use of 'sed' which has been pretty stable
since at
> least 1992 and mostly the same going back to 1974.
>
> Using sed for compatibility with all possible portable releases seems
> 'better' to me than just upgrading a command because POSIX thinks
it is
> a good idea.
This seems like a fine option to me.
> For example:
>
>    head -2 == head -n 2 == sed 'n;q'
Another possibility is `sed 2q`, which works for any number. It's even
mentioned in the rationale section as a way to simulate head(1).
>    tail +3 == tail -n +3 == sed '1,2d'
>
> The sed program has been around a lot longer without these command-line
> semantics changing for POSIX.
>
> These idioms should work fine going back to at least the BSD version of
> sed from 1992 by Diomidis Spinellis and maybe even going back to Lee E.
> McMahon's version in 1974.
>
> @@ -353,7 +353,7 @@ depend-rebuild:
>         rm -f config.h
>         touch config.h
>         makedepend -w1000 -Y. -f .depend *.c 2>/dev/null
> -       (head -2 .depend; tail +3 .depend | sort) >.depend.tmp
> +       (sed 'n;q' .depend; sed '1,2d' .depend | sort)
>.depend.tmp
>         mv .depend.tmp .depend
>         rm -f config.h
>
> The idea of the OpenSSH portable release is to be portable across a LOT
> of UNIX (and even some non-UNIX releases). If that is the goal, why
> enforce the need to fetch and build POSIX-compliant versions of head and
> tail for very old systems?
I think this script is only necessary to rebuild the .depend file,
which is not usually necessary, but you make a good point. I didn't
realize that some implementations did not support the -n option. The
change you suggested sounds good to me.

-Michael

Hi Michael,

Does everything that we care about (which is a lot) do POSIX arguments 
to head and tail?? What systems that do do POSIX don't accept the 
traditional arguments (no "-n".)?

Cheers,

David

On 26/4/20 9:28 pm, David Newall wrote:
> Hi Michael,
>
> Does everything that we care about (which is a lot) do POSIX arguments 
> to head and tail?? What systems that do do POSIX don't accept the 
> traditional arguments (no "-n".)?
>
> Cheers,
>
> David

Question withdraw; already answered.

Hi,

Thanks, but I don't think we're going to merge this one because I'm
somewhat worried that some systems we currently build on do not support
the -n syntax. Conversely, AFAIK everything* supports -number.

-d

* except some GNU tools if you don't set a magic env var, which we do

On Sat, 25 Apr 2020, Michael Forney wrote:
> ---
>  Makefile.in | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/Makefile.in b/Makefile.in
> index 304d96cd..47e04c02 100644
> --- a/Makefile.in
> +++ b/Makefile.in
> @@ -353,7 +353,7 @@ depend-rebuild:
>  	rm -f config.h
>  	touch config.h
>  	makedepend -w1000 -Y. -f .depend *.c 2>/dev/null
> -	(head -2 .depend; tail +3 .depend | sort) >.depend.tmp
> +	(head -n 2 .depend; tail -n +3 .depend | sort) >.depend.tmp
>  	mv .depend.tmp .depend
>  	rm -f config.h
>  
> -- 
> 2.26.2
> 
> _______________________________________________
> openssh-unix-dev mailing list
> openssh-unix-dev at mindrot.org
> https://lists.mindrot.org/mailman/listinfo/openssh-unix-dev
>

Hi Damien,

Damien Miller <djm at mindrot.org> writes:
> Thanks, but I don't think we're going to merge this one because
I'm
> somewhat worried that some systems we currently build on do not support
> the -n syntax. Conversely, AFAIK everything* supports -number.
Michael Forney said that he was trying to run on a system that did NOT
support head -number and tail +number old-style format.

This is why I suggested use of 'sed' instead of 'head' and
'tail'. The
sed command predates both head and tail and the following idiom in sed
should be common going back to at least 1984 when I used sed in this way
on the following systems:

   Berkeley Software Distribution (4.4 BSD-Lite).
   Mt Xinu 4.3
   AIX 3 (1989) - AIX 4 (1994)
   HP/UX System V (1989)
   SunOS 3.0Beta1 (1986) thru Soliars 11
   FreeBSD 2.2.6 thru FreeBSD/11
   OpenBSD 2.7
   Cray X/MP

I recommend the change from

     (head -2 .depend; tail +3 .depend | sort) >.depend.tmp

to

     (sed 2q .depend; sed 1,2d .depend | sort) > .depend.tmp

should do the job correctly for all instances of sed I have ever used.

Failing this solution, coming up with a 'configure' script test might be
possible that provides for a compatibility test for using of -n options
for head and tail

	Be safe, stay healthy,
	-- Mark