Odd need: to track down NUL bytes

[Kevin O'Gorman]

Thanks, I chose a slightly different way to go
1. I wrote a very small program to copy everything up to the first NUL
byte, and report if anything after that was non-NUL (nothing was).
2. I ran it on all files, with output to a different directory
3. Checked that the last line was intact in each file (all but 2 were fine).
4. Computed what work was finished and what was not.
5. Resumed where it left off.

It had run for about 60 days before the crash.  Each line is a separate
problem solved, and each takes at most 30 minutes.  Yes that means I have
millions of problems and answers.  It's a big hobby.  I salvaged a lot of
work this way.



On Sun, Feb 5, 2017 at 11:35 AM, Nils Kassube <kassube at gmx.net> wrote:

> Kevin O'Gorman wrote:
> > I now discover that some files that were under construction at that
> > time are corrupted with extensive NUL bytes.  These are usually text
> > files.  I want to find all such files and "cleanse" them to recover
> > what information I can.  With just about anything _except_ a NUL byte
> > this would be easy, but due to the special treatment of NUL in
> > strings, it's not that clear to me how best to even search for those
> > bytes.
>
> Well, I also don't know how to search for those files, but you could at
> least remove the NUL bytes with something like this:
>
> cat infile | tr -d '\0' >outfile
>
> Or perhaps you prefer to replace the NUL bytes with something else, like
> space - that would be like this:
>
> cat infile | tr '\0' ' ' >outfile
>
> Now, you could just do this operation for all files, regardles if they
> contain NUL bytes:
>
> for f in *;do test -f "$f" && cat "$f" | tr '\0' ' ' >"outdir/$f";done
>
> This would place a copy of each file in the existing folder "outdir"
> with the NUL bytes replaced by spaces (if there are any).
>
>
> Nils
>
>
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-- 
Kevin O'Gorman
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