Regular Expressions and Commands HowTo

Follow me!

ScreenShots

Latest Posts

Comments or help for... (1)

by dynasty

Mar.08.10

Anything related to ... (1)

by dynasty

Mar.08.10

Syncing Zenoss with ... (4)

by dynasty

Feb.08.10

Help with gfs/fencin... (6)

by dynasty

Jan.30.10

RSH working ; but wa... (2)

by dynasty

Jan.28.10

Newest Downloads

snmp_branch.py

Mar.09

Zenoss_Template_Manager

Mar.08

[zenoss@zenoss2 ~]$ python Zenoss_Template_Manager.py -husage: Examples: python Zenoss_Templa...

Get Netscaler Stats

Feb.07

Query NS

Feb.01

python queryns.py -husage: queryns.py [options] arg --username=username --password=password --net...

Swatch Startup Script

Nov.12

Regular Expressions and Commands HowTo

Linux HowTo's - Advance Linux HowTo's

Written by Allen Sanabria

Sunday, 18 May 2008 16:33

Tags:

There are a bunch of great regular expressions HowTo's out there..... Now you may be asking why am I creating another??? Well quite simple, I am creating this one because this is not really just a regular expression howto but more a regular expression HowTo with its everyday uses with linux/unix commands. So it will not cover perl/python/ruby/...etc programming languages regular expressions (That will be for another tutorial :) )

To start this off I will give you a basic introduction to regular expressions using the output
of "ls" and piping it "grep" using the -oE options (The o stands for Exact match and the E stands for Extended Regular Expressions). Using "(BRE and ERE) Basic Regular Expressions and Posix Extended Regular Expressions"...

THIS IS NOT A TUTORIAL BUT A HOWTO!! So this means more examples and less explaining..

Anchors	What it means	Example
^	Start of string	ls \|grep -oE "^C\w+\.jpg" Chunka.jpg Chunka1.jpg
$	End of string	ls \|grep -oE "\w+(\.jpg$)" Chunka.jpg Chunka1.jpg DSCF0732.jpg
\b	Word boundary	ls \|grep -oE "\bChunka\b\.jpg" Chunka.jpg
\<	Start of word	ls \|grep -oE "\<Ch\w+\.jpg" Chunka.jpg Chunka1.jpg
\>	End of word	ls Scripts/Python/ \|grep -oE "\w+\>\.py" xen_mac_generate.py

Character Classes	What it means	Example
\w	Word	ls \| grep -oE "\w" C C
\W	Non word	ls \|grep -oE "\W" . .

Quantifiers	what it means	example
*	zero or more times	*ls \| grep -oE "\w.jpg"** Chunka.jpg Chunka1.jpg DSCF0732.jpg
+	one or more times	ls \| grep -oE "\w+" Chunka Chunka1 DSCF0732
?	matches either once or zero times	ls \| grep -oE "Chunka1?.jpg" Chunka.jpg Chunka1.jpg
{2}	Exactly 2 times	ls \| grep -oE "(^C{2}h\w+.jpg)" CChunka.jpg
{1,}	1 or more times	ls \| grep -oE "(^C{1,}h\w+.jpg)" CChunka.jpg CCChunka.jpg Chunka.jpg Chunka1.jpg Chunka11.jpg
{1,2}	1 through 2 times	ls \| grep -oE "(^C{1,2}h\w+.jpg)" CChunka.jpg Chunka.jpg Chunka1.jpg Chunka11.jpg