Passing the output of the last command to sed as an argument

Question

Basically, I'm wanting to automate adding something to xorg.conf in the right place, I've used some commands to get the line number of the line I want to manipulate, but I'm not really sure how to go about passing this line number (as an argument and NOT something to be manipulated) to sed. I have been told about xargs and looked at the docs on it, but after some reading and experimentation I can't seem to get it to work.

In case anyone can think of a better method entirely, the process I want to automate is just finding the line containing both "Identifier" and "Monitor0" (there will only be one) and adding a line below it. The problem with just finding Monitor0 and manipulating that line is that there are multiple lines with Monitor0 in.

I've got this far:

fgrep -n "Monitor0" </etc/X11/xorg.conf | fgrep "Identifier" | cut -f1 -d:

This gives out the line number which I'm wanting to pass to sed, but I'm not really sure how to do it.

...or is there a simpler way which I'm not seeing?

Answer 1

I can think of a framework to do this in a perl script, but i don't have that have experience with sed so you would have to take core of the details.

Write a perl script which first identifies the line (not the line number) at which you have to append. (Something like: $line = system("fgrep -n ..."); ) Then run sed like this:sed s/$line/$line.'\n'.$linetoadd/ <$oldfile >$newfile.

Answer 2

Sorted it (thanks #cogs on SynIRC), solution for this particular issue is as follows:

sed '/\bIdentifier\b.*\bMonitor0\b/ a\\tOption "NoDDC"'