egrep grep regex

First if you want the full capabilities in grep you have to run it with -E flag or go for egrep

Flags

Flag	Description
-i	ignores case
-v	return all lines which don’t match pattern (not matching)
-w	The expression is searched for as a word (as if surrounded by [[:<:]]' and [[:>:]]’
-c	count of matching lines
-l	print the name of the file with the match
-n	print the line number
-r	recursively read all the files in the location
-o	only matching

RegEx Syntax

Symbol	Description
[abc]	range, i.e. any of a b c
[^abc]	not range, i.e. not any of a b c
(abc)	group, can be then used later on
\n
|	or, the logical operator
\\,\*	removes the special meaning of a character

RegEx Locations and Anchors

Symbol	Description
^	beginning of the line
$	end of the line
\<	beginning of the word
/>	end of the word
\b	match either beginning or end of a word

RegEx Multipliers

Symbol	Description
?	optional (matched 0 or 1 times)
*	Kleene star (matched 0 or infinite times)
+	Kleene plus (matched 1 or infinite times)
{n}	matched n times
{n,}	matched n times or more
{n,m}	matched between n times and m times

Used Often + examples

egrep -o '([0-9]+\.){3}([0-9]+)' | sort --unique - IPV4 pipe that only displays unique entries