echo do not print NUL byte

echo do not print NUL byte

[Trek]

there is no way to print the NUL byte with the echo utility

with an XSI shell (mksh, posh, yash):

  $ sh -c 'echo \\0 | od -An -c'
    \0  \n

with a shell that requires echo -e (ksh, bash, busybox, mksh):

  $ sh -c 'echo -e \\0 | od -An -c'
    \0  \n

with dash (XSI, no -e argument):

  $ dash -c 'echo \\0 | od -An -c'
    \n

where others characters are correctly printed:

  $ dash -c 'echo \\0100 | od -An -c'
     @  \n

with dash it only works with printf:

  $ dash -c 'printf \\0\\n | od -An -c'
    \0  \n


I discovered this bug developing a small shell library, where you can
find an use case in the n_bytes_encode function of the lib/bytes.sh file
included in http://www.trek.eu.org/devel/naive/naive-0.0.2.tar.gz

c-ya!

Re: echo do not print NUL byte

[Eric Blake]

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On 01/20/2016 02:38 PM, Trek wrote:
> there is no way to print the NUL byte with the echo utility

POSIX says you should use 'printf', not 'echo', if you expect to use any
\ in the arguments.  That said, the man page says:

     echo [-n] args...
...
            \0digits
                    Output the character whose value is given by zero to
three
                    octal digits.  If there are zero digits, a nul character
                    is output.


> with dash (XSI, no -e argument):
> 
>   $ dash -c 'echo \\0 | od -An -c'
>     \n

So this is behavior in disagreement with the documentation, so you
definitely have discovered a bug.  Of course, since POSIX already says
the use of \ is implementation-defined if XSI is not in force, and dash
doesn't necessarily strive for full XSI compliance, it might be easier
to patch the docs than to output a NUL byte.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: echo do not print NUL byte

[Harald van Dijk]

Hi,

On 20/01/2016 22:38, Trek wrote:
> there is no way to print the NUL byte with the echo utility
>
> with dash (XSI, no -e argument):
>
>    $ dash -c 'echo \\0 | od -An -c'
>      \n

This is https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=379227, which 
did get fixed already, but it was after 0.5.8. That should mean it will 
be in the next release of dash, but you can check out the sources from 
Git if you want to see it now.

Cheers,
Harald van Dijk

Re: echo do not print NUL byte

[Trek]

On Wed, 20 Jan 2016 23:32:11 +0100
Harald van Dijk <harald@gigawatt.nl> wrote:

> This is https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=379227,
> which did get fixed already, but it was after 0.5.8.

happy to see that it is already fixed and sorry for double reporting

Re: echo do not print NUL byte

[Bastian Bittorf]

* Trek <trek00@inbox.ru> [21.01.2016 07:06]:
> included in http://www.trek.eu.org/devel/naive/naive-0.0.2.tar.gz

interesting! can you switch to git or another CVS?

bye, bastian