Cat changes owner? - linux

Question

I have to edit a file owned by root via ssh. I add a entry in the file, preserve the first 9 lines and reorder the rest to a temporary file. I know that > overwrittes what's in the file (and that's what i want) but I need to preserve the root as owner of file. How can I do this? Thanks!
#!/bin/bash
user=""
echo "User:"
read user
ssh xxxx#xxxx "
sed -i '\$a$user' file;
(head -n 9 file ; tail -n +10 file | sort) > temp;
cat temp > file;
rm -f temp
"

Answer 1

It's not cat that's changing the owner, it's sed. When you use sed -i, it does something like:
mv file file.bak
sed '\$a$user' file.bak > file
rm file.bak
As you can see, this creates a new file with the original file's name, and it's owned by the user that creates the file.
If you want to avoid this, make a copy of the original file instead of using the -i option.
cp file /tmp/file.$$
sed '\$a$user' /tmp/file.$$ > file
rm /tmp/file.$$
Or you could just put sed into your pipeline:
sed '\$a$user' file | head -n 9 file ; tail -n +10 file | sort > temp
cat temp > file
rm temp

Answer 2

Been a while since I wrote in BASH but i think a starting point would be
chown root $file // if you have a variable with the file name in
or
chown root thefile.txt //if you want it hard coded;
another variable in the equation would be who has ownership of the application cat? i think whoever is the owner of the running application, thats how the ownership of the files its out put is decided
maybe you could also try
$ sudo cat temp > file
because the session would then belong to the root and therefore the ouput would belong to the root???

Answer 3

I take it that the user who logs in cannot become root?
THen your best bet is to use dd
dd if=tmpfile of=outfile
of course, do all the ordering, seding, awking and greping on your tmp file. dd in this usage is equivalent > without creating a new file

Answer 4

#!/bin/bash
user=""
echo "User:"
read user
ssh xxxx#xxxx "
sed -i '\$a$user' file;
(head -n 9 file ; tail -n +10 file | sort) > temp;
sudo mv temp file;
sudo chown root file
"
This will work better if on the xxxx machine the xxxx user you're logging in as has password-less access to sudo. You can do this by having this entry in your /etc/sudoers file there:
xxxx ALL=NOPASSWD: ALL