Re: Sed and redirection into the same file

On Friday 29 September 2006 15:53, Joshua Bassett wrote:

> It all appears to work fine, but the problem is when redirecting the
> output back into the same file...I end up with empty files! For
> example, the following works fine:
>
> for x in `grep -lr 'foo' app | grep -v "svn"`; do sed 's/foo/bar/'
> <${x} >${x}.new; done
>
> Clearly it's something to do with the <${x} >${x} part. What am I missing
> here?

You can't do in-place file edits with sed.  Stick with what you found to work 
and just rename the .new file if it's non-zero in size otherwise delete it.  
e.g:

for x in `grep -lr 'foo' app | grep -v "svn"`
do
sed 's/foo/bar/'<${x} >${x}.new
if [ -s ${x}.new ]; then
   mv ${x}.new ${x}
else 
    rm -f ${x}.new
fi
done


otherwise, use a perl one-liner (eg. perl -pie 's/foo/bar/').  Perl's -i 
switch will do in-place file edits for you.

Cheers,

- brendon.

-- 
No man is useless who has a friend, and if we are loved we are indispensable.
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