$ curl cheat.sh/
# grep
# Matches patterns in input text.
# Supports simple patterns and regular expressions.

# Search for an exact string:
grep search_string path/to/file

# Search in case-insensitive mode:
grep -i search_string path/to/file

# Search recursively (ignoring non-text files) in current directory for an exact string:
grep -RI search_string .

# Use extended regular expressions (supporting `?`, `+`, `{}`, `()` and `|`):
grep -E ^regex$ path/to/file

# Print 3 lines of [C]ontext around, [B]efore, or [A]fter each match:
grep -C|B|A 3 search_string path/to/file

# Print file name with the corresponding line number for each match:
grep -Hn search_string path/to/file

# Use the standard input instead of a file:
cat path/to/file | grep search_string

# Invert match for excluding specific strings:
grep -v search_string

$
Follow @igor_chubin cheat.sh tldr