BASH > grep

grep <options> pattern <file...>

Matching options

-e, --regexp=PATTERN
-f, --file=FILE
-i # ignore-case
-v, --invert-match
-w, --word-regexp
-x, --line-regexp

Pattern options

-F  # list of fixed strings
-G  # basic regular expression (default)
-E  # extended regular expression

REGEX

caracters have a special meaning unless they are escaped with a backslash: ^ $ . * [ ] \

caracters do not have any special meaning unless they are escaped with a backslash: ? + { } | ( )

-E caracters a special meaning unless they are escaped with a backslash: ^ $ . * + ? [ ] ( ) | { }

Output Options

-c  # print the count of matching lines. suppresses normal output
-m, --max-count=NUM   # stop reading after max count is reached
-o  # only print the matched part of a line
-q  # quiet, silent
-s  # suppress error messages about nonexistent or unreadable files

Context Options

-B NUM  # print NUM lines before a match
-A NUM  # print NUM lines after a match
-C NUM  # print NUM lines before and after a match

Examples

grep -E "foo|oof" bar.txt # match any line in bar.txt that contains either "foo" or "oof"

# match anything that resembles a URL in foo.txt and only print out the match
grep -oE "https?:\/\/((\w+[_-]?)+\.?)+" foo.txt

# follow the tail of server.log, pipe to grep and print out any line that contains "error"
# and include 5 lines of context
tail -f server.log | grep -iC 5 error