Hi All

I am trying to change the text "root" from a file to "#root". When i am
running the following command on the prompt but without redirection it
is displaying the correct output on the terminal. But when i redirect
the output to the same file the file loses all its contents.

Pls .

sed '1,$s/root/#root/' /etc/ftpd/ftpusers > /etc/ftpd/ftpusers

Thanks
Manish.

manish wrote:
> Hi All
>
> I am trying to change the text "root" from a file to "#root". When i am
> running the following command on the prompt but without redirection it
> is displaying the correct output on the terminal. But when i redirect
> the output to the same file the file loses all its contents.
>
> Pls .
>
> sed '1,$s/root/#root/' /etc/ftpd/ftpusers > /etc/ftpd/ftpusers
>
> Thanks
> Manish.

Then direct the output to a new file with a different name and
afterwards "mv" it over the old file.

Hi,
You cannot redirect it to the same file.
You will need to redirect to a temp file and then rename that temp
file.
Else open the file in vi and do a search-replace
Hope this s.

Thanks & Regards,
Amit S. Dabri

manish wrote:
> Hi All
>
> I am trying to change the text "root" from a file to "#root". When i am
> running the following command on the prompt but without redirection it
> is displaying the correct output on the terminal. But when i redirect
> the output to the same file the file loses all its contents.
>
> Pls .
>
> sed '1,$s/root/#root/' /etc/ftpd/ftpusers > /etc/ftpd/ftpusers
>
> Thanks
> Manish.

RolandRB wrote:
> manish wrote:
>> Hi All
>>
>> I am trying to change the text "root" from a file to "#root". When i am
>> running the following command on the prompt but without redirection it
>> is displaying the correct output on the terminal. But when i redirect
>> the output to the same file the file loses all its contents.
>>
>> Pls .
>>
>> sed '1,$s/root/#root/' /etc/ftpd/ftpusers > /etc/ftpd/ftpusers
>>
>> Thanks
>> Manish.
>
> Then direct the output to a new file with a different name and
> afterwards "mv" it over the old file.
>

For safety reasons (e.g. retaining the permissions),
I recommend to not mv, instead do cp then rm.

e.g.

sed '/root/#root/' /etc/ftp/ptpusers > /etc/ftpd/ftpusers.tmp &&
cp /etc/ftpd/ftpusers.tmp /etc/ftpd/ftpusers &&
rm /etc/ftpd/ftpusers.tmp

Alternatively, if you want to keep a .old file:

cp -p /etc/ftpd/ftpusers /etc/ftpd/ftpusers.old &&
sed '/root/#root/' /etc/ftp/ptpusers.old > /etc/ftpd/ftpusers

The && at the end of the line ensures that the next lines are
only run when the exit status is zero.


--
Michael Tosch @ hp : com

it works now...

thanks to you all for ur .

Bye

manish wrote:
> is displaying the correct output on the terminal. But when i redirect
> the output to the same file the file loses all its contents.
> sed '1,$s/root/#root/' /etc/ftpd/ftpusers > /etc/ftpd/ftpusers
This is a fairly common error, similar to attempting to do:
sort file > file
The problem with these is the shell first does the redirection,
so the output file is opened and trucated. The command then executes,
producing no output, thus one ends up with an empty file. Using >>
instead of > also won't solve the problem, as in that case - depending
on factors such as buffering - one may end up with a very large file,
as one has effectively created an infinite loop.