regex: grep/egrep cheatsheet

egrep grep regex

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


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
| 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