tail -f /myFile.log | grep 'string_to_find'

# for a log file
# 1: hello
# 2: string_to_find on line 2
# 3: hello again

# the command above will output: 
# string_to_find on line 2

# to do an invert match just use -v with grep
# tail -f /myFile.log | grep -v 'string_to_ignore'

When tailing a log file, its sometimes handy to only show parts of it that you are interested in, this simple pipe does the job.

Filter the output of a tail

filter

Bash