grep

Search all lines with specified string in a file

grep "string" test.txt

Search all lines with specified string in a file pattern (test_1.txt, test_2.txt, test_3.txt ...)

grep "string" test_*.txt

Case insensitive search all lines with specified string in a file

grep -i "string" test.txt

match regex in files (*)

grep "REGEX" test.txt

Match lines with the pattern starts with "first" and ends with "last" with anything in-between

grep "start.*end" test.txt

search for full words, not for sub-strings

grep -iw "is" test.txt

display line matches the pattern and N lines after match

grep -A 3 "string" test.txt

display line matches the pattern and N lines before match

grep -B 2 "string" test.txt

display line matches the pattern and N lines before match and N lines after match

grep -C 2 "string" test.txt

search all files recursively

grep -r "string" *

display all lines that doesn’t match the given pattern

grep -v "string" test.txt

display lines that doesn’t match all the given pattern (if there are more than one pattern)

grep -v -e "string1" -v -e "string2" test.txt

count the number of lines that matches the pattern

grep -c "string" test.txt

count the number of lines that don’t match the pattern

grep -v -c "string" test.txt

display only the filenames containing the given pattern (test_1.txt, test_2.txt, test_3.txt ...)

grep -l "string" test_*.txt

Show only the matched string, not the whole line

grep -o "start.*end" test.txt

show line number while displaying the output

grep -n "string" test.txt

• (*) Regex: ? The preceding item is optional and matched at most once.

• The preceding item will be matched zero or more times.

• The preceding item will be matched one or more times. {n} The preceding item is matched exactly n times. {n,} The preceding item is matched n or more times. {,m} The preceding item is matched at most m times. {n,m} The preceding item is matched at least n times, but not more than m times.

Credit:

Bash-Fu/grep at master · areyou1or0/Bash-FuGitHub

• Useful Regex

Find mac addresses

cat file1 | sed -e 's/^.*\([a-fA-F0-9]\{12\}\).*$/\1/'

Find ip addresses

cat file1 | grep -Eo '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'