Grep

ignore commented and empty lines

grep -v "^#\|^$"  /path/to/dir

count number of empty lines

grep -c "^$"  ..

only IP address

grep -Eo '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'

returning lines before and after match (e.g. ‘bbo’)

# return also 3 lines after match
grep -A 3 'bbo'

# return also 3 lines before match
grep -B 3 'bbo'

# return also 3 lines before and after match
grep -C 3 'bbo'

lines without word (e.g. ‘bbo’)

grep -v bbo filename

grep all content of a fileA from fileB

grep -f fileA fileB