file redirect is destroying the file ? Help!
dave.list at pixelhammer.com
Mon Oct 30 15:51:09 UTC 2006
Ensel Sharon wrote:
> I have a script that, among other things, removes a line from
> I do this with this method:
> cat /etc/ftpchroot | grep -v $remove > /etc/ftpchroot
> Easy. You cat all of the file except the line you want to remove, and
> redirect it back to itself.
> The problem is, about 50% of the time, I end up with an empty ftpchroot
> file. It is zero bytes. This obviously has nothing to do with a bad
> variable, since if it wasn't there, the starting file and ending file
> would just be identical.
> Instead, I get an empty file. I have reproduced this with other files in
> other places - works some of the time, other times gives me an empty file.
> What gives ?
> (note, I know a lot of ways to work around this - so I'm not so much
> asking how to fix this, as I am asking "why does this happen" ?)
I can't answer your question except to say that I have always redirected
to a tmp file, and then replaced the original after safely closing it
and testing the tmp file for whatever results I expect.
Just dumping output to overwrite the file I am currently reading was
always bad juju in my book.
Three years now I've asked Google why they don't have a
logo change for Memorial Day. Why do they choose to do logos
for other non-international holidays, but nothing for
Maybe they forgot who made that choice possible.
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