grep for ascii nul

[David Christensen]

On 11/1/19 11:45 PM, Victor Sudakov wrote:
> Ronald F. Guilmette wrote:
>> In message <20191101092716.GA67658 at admin.sibptus.ru>,
>> Victor Sudakov <vas at sibptus.ru> wrote:
>>
>>> I need to find files containing ascii null inside, and print their names to
>>> stdout.
>>
>> Unfortunately, you're banging up against a long-standing a rather
>> annoying non-feature of fgrep/grep/egrep, which is that unlike the
>> tr command, the grep family of commands does not support the \DDD
>> notation for specifying arbitrary byte values.  Thus, you cannot use
>> then to search for arbitrary byte values.
>>
>> I would thus suggest that you solve your problem using a Perl or C
>> program.
> 
> Perl is not in the base system, so that is not quite the answer.
> I'm a big fan of awk, awk is in the base system and should be able to do
> it, right?
> 
> $ hd trees.txt
> 00000000  66 69 72 0a 6f 61 6b 0a  63 65 64 00 61 72 0a 62  |fir.oak.ced.ar.b|
> 00000010  69 72 63 68 0a 70 61 6c  6d 0a                    |irch.palm.|
> 0000001a
> $
> 
> Note the ascii null embedded in the word "cedar"
> 
> $ awk '/\x66\x69/{print $0}' trees.txt
> fir
> 
> So far so good. But with the ascii nul it behaves in an unexpected way:
> 
> $ awk '/\x00/{print $0}' trees.txt
> fir
> oak
> ced
> birch
> palm
> $
> 
> 

2019-11-03 02:16:02 freebsd at fbsd112 ~/sandbox/sh
$ freebsd-version ; uname -a
11.2-RELEASE
FreeBSD fbsd112 11.2-RELEASE FreeBSD 11.2-RELEASE #0 r335510: Fri Jun 22 
04:32:14 UTC 2018 
root at releng2.nyi.freebsd.org:/usr/obj/usr/src/sys/GENERIC  amd64


Perl is one of the first things I install on FreeBSD systems:

root at fbsd112:~ # pkg install perl5
Updating FreeBSD repository catalogue...
FreeBSD repository is up to date.
All repositories are up to date.
The following 1 package(s) will be affected (of 0 checked):

New packages to be INSTALLED:
	perl5: 5.30.0

Number of packages to be installed: 1

The process will require 58 MiB more space.
14 MiB to be downloaded.

<snip>


Solving your problem then becomes a Perl one-liner:

2019-11-03 02:16:11 freebsd at fbsd112 ~/sandbox/sh
$ hd hello.txt
00000000  68 65 6c 6c 6f 2c 20 77  6f 72 6c 64 21 0a        |hello, world!.|
0000000e

2019-11-03 02:16:31 freebsd at fbsd112 ~/sandbox/sh
$ hd trees.txt
00000000  66 69 72 0a 6f 61 6b 0a  63 65 64 00 61 72 0a 62 
|fir.oak.ced.ar.b|
00000010  69 72 63 68 0a 70 61 6c  6d 0a                    |irch.palm.|
0000001a

2019-11-03 02:16:35 freebsd at fbsd112 ~/sandbox/sh
$ cat find-files-with-nul.sh
#!/bin/sh
perl -e 'while (<>) {$f{$ARGV}++ if /\x00/}; print keys %f' $@

2019-11-03 02:16:39 freebsd at fbsd112 ~/sandbox/sh
$ sh find-files-with-nul.sh hello.txt trees.txt
trees.txt


David