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Redirect overwrites itself

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# 1  
Old 05-21-2010
Redirect overwrites itself
I bet many people faced this problem before:

The command below will result in a blank file:

Code:
$ cat myfile | grep pattern > myfile

Is there any easy way to do it?
# 2  
Old 05-21-2010
Yes. Don't do it Smilie

Write to another file, and copy the new file over the old one if you have to.
# 3  
Old 05-21-2010
Quote:
Originally Posted by scottn
Yes. Don't do it Smilie

Write to another file, and copy the new file over the old one if you have to.
I've always done that, but it seems like a waste of time.
There has to be a general solution for this problem. SmilieSmilieSmilieSmilieSmilie
# 4  
Old 05-21-2010
Code:
sed -ix -n "/pattern/p" file1

# 5  
Old 05-21-2010
Code:
sed -ie '/pattern/!d' myfile

Handle with care! Smilie
# 6  
Old 05-21-2010
Grep was just an example. Let's say I'm editing the file with tr,cut,awk,etc.
We can't rely on sed for everything.

Ps: thanks a lot for your response Scottn, but I believe there has to be a better way.
# 7  
Old 05-21-2010
The sed ways shown above is the GNU sed way - not the (for my two cent's worth) standard way.

The other tools that you mention, GNU or otherwise, most likely don't have that "flexibility".
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