[SOLVED] insert text before the First Pattern Found

NetRock · 04-08-2011, 11:04 AM

Hi
i need to add this line
nameserver 208.67.122.221 from ISP before the first nameserver already exists in resolv.conf in all workstations i know

Code:

sed '/nameserver/ i\nameserver 208.67.122.221'

but that insert it on every line after nameserver not only before the first one

Code:

# blah blah
# blah blah
domain mydom.com
nameserver 111.114.110.21
nameserver 111.116.66.21
nameserver 111.117.120.21
.......... ..............
.........  ..............
# blah blah

Thank you for your help.

David the H. · 04-08-2011, 11:40 AM

Try this.

Code:

sed '0,/nameserver/ { /nameserver/i nameserver 208.67.122.221
}' file

First, match from start-of-file to nameserver, then match again inside that selection. Unfortunately though, the a,i,c commands terminate on newlines, so you have to physically break the line in order to finish up the expression.

Your shell allows a bit of a trick though that will allow you to do it on one line:

Code:

sed $'0,/nameserver/ { /nameserver/i nameserver 208.67.122.221 \n }' file

$'..' is an extended quoting system that expands backslashed characters like \n, similar to echo -e.

Edit: Here's another way to do it that doesn't require as much thinking:

Code:

sed -r "0,/nameserver/ s/(.*nameserver.*)/nameserver 208.67.122.221\n\1/" file

grail · 04-08-2011, 11:41 AM

Not sure with sed. There is a 'q' for quitting but then I could only get to first nameserver and it stopped

Code:

awk '!a && /nameserver/{print "nameserver 208.67.122.221";a=1}1' file

NetRock · 04-08-2011, 12:22 PM

Thanks for your replies.
All i need it just get to the first nameserver in the file and modify the file, That's ALL
so from:

Quote:

# blah blah
# blah blah
domain mydom.com
nameserver 111.114.110.21
nameserver 111.116.66.21
nameserver 111.117.120.21
.......... ..............
......... ..............
# blah blah

to this:

Quote:

# blah blah
# blah blah
domain mydom.com
nameserver 208.67.122.221
nameserver 111.114.110.21
nameserver 111.116.66.21
nameserver 111.117.120.21
.......... ..............
......... ..............
# blah blah