Replace exact part of text in a string (fstab) using sed

Question

I'm in the process of migrating some data between 2 servers. The data is held in the same folder structure on each server.

Once the data has been moved I want to update the fstab file on all of the affected Linux machines. I have a bash script that rsyncs the data between the servers and then logs on to each machine in a list and updates the fstab with the new IP address using sed.

sed "s/\(172.16.0.30\)\(.*\)\(${share}\)\(.*\)/172.16.0.35\2\3\4/"

This has worked absolutely fine in the past, however this time I'm migrating a folder which has a name very similar to a few others, let's say $share is 'home':

home
home-old
home-ancient

The problem I'm having is that this regex is picking up all of the shares with the text contained in $share and not just the one I want.

Is there a way to adjust the regex so that it will only replace the IP on the single line that I want? I've looked at the /b variable but can't seem to get it to work, unfortunately regular expressions usually confuse me!

Answer 1

\\b is a GNU extension and in this case won't work because it matches a word boundary, and both the space and - are in the group of non-word. It will match all of them. One simple option is to match a space (or end-of-line) character after $share , like:

sed "s/\(172.16.0.30\)\(.*\)\(${share}\)\( \(.*\)\|$\)/172.16.0.35\2\3\4/"