cat and grep without destroying file

[Chris Malton]

(``-_-´´) -- Fernando wrote:
> I've been trying to make a small shell script that would remove a line from a text file.
> But every time that I pipe the content of grep to the original file, the file ends up blank.
> So, I've made the script use a copy and them replace the original.
> It looks like this:
> #for i in $(/bin/ls -1); do cat $i | egrep -v ^Date > $i.new; mv $i.new $i; done
> 
> Isn't there any other way, without using the mv?
> 
> 

I don't think so, some how.  I have never successfully done it without 
an mv or a cp.

Chris