So you want something that will match server another-ip-or-hostname-here [burst iburst] for all values of another-ip-or-hostname-here except 127.127.1.0 and doesn't match if the line includes prefer, wiping the line on match? You can accomplish this fairly easily with negative look-ahead assertions.

perl -p -i -e 's/server (?!\Q127.127.1.0\E)[\w\.]+\s+(?!prefer).*//g' ntp.conf

See perlretut for more info. And might I suggest -i.bak in place of -i?

In reply to Re: Regexp to exclude one IP and get all others? by kennethk
in thread Regexp to exclude one IP and get all others? by bowei_99

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