Regular Expressions in Linux

Regular Expression:

[.] DOT	dot matches for a single character
[abcd]	matches one of the list ,say [abcd] matches one of a,b,c,d
[a-d]	matches the range of characters a to d
[^a-i]	should not contain the range a to i
[a*] ~= {0,}	match zero or more a’s
[a+] ~= {1,}	match one or more a’s
[a?] ~= {0,1}	zero or one occurance of letter a
wh(at|en|ere}	what when where , you can specify group of letters and also a pipe to mark OR operator
^not	start with string not,notify,notice etc……
not$	end with not like knot

 

GREP: search Globally for Regular Expression and Print

grep	option[s]
	-n number in the file
	-c count the number of occurrences, unlike wc –l it gives the file wise count
	-A context selection After -B Context selection Before you can specify number with A or B
	-l List the names of files
	-r recursively Grep
	-s , if there are permission errors it suppresses
	-e used to search multiple regular expressions

Egrep: Extended GREP { More operators +,?,(),|}

Fgrep: Fixed length Grep , does not support operators