Regular Expressions and Commands HowTo

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Regular Expressions and Commands HowTo

Linux HowTo's - Advance Linux HowTo's

Written by Allen Sanabria

Sunday, 18 May 2008 16:33

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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