Grep Cheatsheet - Notes from Linuxize

Posted on Jan 9, 2021 2 mins

Grep

Table of Contents

References

Manual Link
Derived from Linuxize

(GNU) Grep supports 3 forms of regex

Basic - This is default
Extended - -E or --extended-regexp
Perl-campatible - -P or --perl-regexp

Basic vs Extended

meta chars ?,+,{,|,(,) have to prepended with \ in basic but not in extented.
There are some more minor subtle diff - here

Ex Basic: grep 'b\?right' Extended: grep -E 'b?right' This will match both brignt and right

Cheatsheet

Stright match

grep string file

Anchors

Metachar	Meaning	Example	Result
`^`	First	`^linux`	will match `linux` but not `alinux`
`$`	Last	`linux$`	will match `linux` but not `linux mint`

Objects

Pattern	Meaning
`.`	Any single char
`[ab]`	Either a or b
`[abc]`	Either a or b or c
`[^l]`	Single char other than l
`[^abc]`	Single char that is niether a nor b nor c
`[A-Z]`	Capital chars from A to Z
`[a-m]`	small chars from a to m
`[0-5]`	single number from 0 to 5
`[:alnum:]`	Alphanumeric Chars same as `[0-9A-Za-z]`
`[:alpha:]`	Alphabetic Chars
`[:blank:]`	Space and Tab
`[:digit:]`	Digits `[0-9]`
`[:space:]`	Space char
`[:lower:]`	Lower char
`[:upper:]`	Upper char

Complete list can be found here Grep Manual

Repeaters

Metachat	Meaning
`*`	Match the preceding item zero or more times
`?`	Match the preceding item zero or one times
`+`	Match the preceding item one or more times
`{n}`	Match the preceding item exactly n times
`{n,}`	Match the preceding item at least n times
`{,n}`	Match the preceding item at most n times
`{n,m}`	Match the preceding item from n to m times

OR(|) operator

Format	Meaning
`<expr1>\|<expr2>`	Either `<expr1>` or `<expr2>`

Note: This needs to be preceded with \ in Basic regex Example: Basic: grep dogs\?\|cats\? - This will match dog. dogs, cat and cats Extended: grep -E dogs?|cats?

Grouping

Format	Meaning
`(<regexp>)`	`<regexp>` when enclosed with `()` are considered as single item, useful with Repeaters

Example: grep -E 'John(athan)?$' - Will both John and Johnathan