Linux – Cannot cat file which has space in name in linux

I don't know if this is what you are looking for but you might try this:

grep "pattern you are looking for" log.txt;tail -n 0 -f log.txt | grep "pattern you are looking for"

it's calling two commands one after another. first you grep the pattern you are interested in from the log file and then you start tail -f at the end of the file redirecting output to grep.

however I suggest you do it using one command only, you can specify the number of lines to be displayed by tail using -n parameter (+1 means from the first line):

tail -n +1 -f log.txt | grep "pattern you are looking for"