Grep regex NOT containing string

Question

I am passing a list of regex patterns to grep to check against a syslog file. They are usually matching an IP address and log entry;

grep "1         


        

Answer 1

(?

You need to run this with -P to have negative lookbehind (Perl regular expression), so the command is:

grep -P '(?

Try this. It uses negative lookbehind to ignore the line if it is preceeded by 1.2.3.4. Hope that helps!