Count line when words have been matched:

$ grep -c 'word' /path/to/file

Pass the -n option to precede each line of output with the number of the line in the text file:

$ grep -n 'root' /etc/passwd

Ignore word case:

$ grep -i 'word' /path/to/file

Use grep recursively under each directory:

$ grep -r 'word' /path/to/file

Use grep to search 2 different words:

$ egrep -w 'word1|word2' /path/to/file

Grep invert match:

$ grep -v 'word' /path/to/file

You can force grep to display output in colors, enter:

$ grep --color 'word' /path/to/file

You can limit the results count:

$ grep -m 10 'word' /path/to/file

You can match regular expression in files (Syntax: grep "REGEX" filename):

$ grep 'word1.*word2' /path/to/file

• ? 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.

Display N lines Around Match

Grep can display N lines after match (Syntax: grep -A <N> "string" filename):

$ grep -A 2 'word' /path/to/file

The following example prints the matched line, along with the two lines after it.

$ grep -A 2 -i 'word' /path/to/file

-C is the option which prints the specified N lines before the match.

$ grep -C 2 'word' /path/to/file