UNIX for Advanced & Expert Users

Hey!!!

Do you really want to create a physical file "valid_servers"? Instead, we can just redirect the output of grep to while loop.

Code:

egrep -v '^#|^$' file1|while read server_name
do
    echo "$server_name"
    # File transfer goes here
done

Cheers,
Ranga

Hi Ranga,
Thanks for your reply,
I had tried this before I post my problem here, too bad it doesn't skip any # in front of the line.

It's good of you to point that out. I already knew that. I was just trying to present a simple solution.

Normally, I prefer to put the input to the while loop at the end, because it seems cleaner and easier to read. And making a separate file makes the intent more clear. It's a way of self-documentation.

Your suggestion related to the blank line is an improvement.

Hey!!!

This will work and look at the highlighted part. before that you have redirected the file to while loop instead of grep.

Code:

egrep -v '^#|^$' server.cfg|while read server_name
do
echo "$server_name"
# File transfer goes here
done

Cheers,
Ranga

Yes. I did try the same thing before.
Still the same.

Please make a try with this now and then post us.

Cheers,
Ranga

---------- Post updated at 04:15 AM ---------- Previous update was at 04:13 AM ----------

Yeah you are right. If the file size is biggy then, you should be rethink of your self documentation!!!

Cheers,
Ranga

No, you did not. Your original attempt is not the same.

What you did:

Code:

grep -v '^#' | while read line; do ... done < server.cfg

What rangarasan suggested:

Code:

grep -v '^#' server.cfg | while read line; do ... done

There is a big difference. Pipe redirections occur before other redirection operations.

rangarasan is telling grep to read the file. Your original solution has grep reading something else (whatever standard input descriptor it inherited, which could be a teriminal or some other file).

You redirected the file directly to the while-read loop, bypassing grep. Your grep is doing nothing. Even if there is something for it to read on standard input (we can't tell from your script what stdin is, since it depends on how the script is called), there is nowhere for the grep data to go. Why? Because after the pipe connects the standard output of grep to the standard input of the while-read loop, the standard input of the while-read loop is overridden by the redirection operation immediately following the while-loop. So, even if grep does write to the pipe, there is nothing on the other end to read the data.

On a different note, there is no need for grep. Within the while-loop, a case statement can do the job:

Code:

case $line in
    \#*) continue ;;
esac

Or, if the shell supports substring parameter expansion:

Code:

[ "${line:0:1}" = '#' ] && continue

Regards,
Alister