Pattern Searching

Commands	Options	Description
/	/Unix	Forward search of Unix keyword in file
?	?Unix	Backward search of Unix keyword in file
n		Repeat the last search
.		Repeat the previous command
:1, $s/<search string>/<Replace String >/g		Pattern search and replacement.
	1,$	Represent all lines in the file.
	g	Stands for globally
:3,10s/gagan/deep/g		search between lines 3 and 10
: .s/gagan/deep/g		Only the current line.
: $s/gagan/deep/g		Only the last line.
: $s/gagan/deep/gc	c	Ask for confirmation for replacement
grep
	-c	counting occurrence.
	-n	display line number for record.
	-v	skip records that contain directory.
	-l	display files containing record.
	-i	ignore case.
	[PQR]	match any single character.
	[c1-c2]	match char with ASCII range
	[^PQR]	match single character which is not PQR.
	^<pat>	beginning with pattern.
	<pat>$	ending with pattern.
	{a-Z A-Z 0-9}	match any single character.
	ls –l |grep “^d”	Prints only directories.
egrep
	egrep '[aA]g+[ar][ar]wal' test1.txt	match one or more occurrence matches ag & agg.
	egrep '[aA]gg?[ar][ar]wal' test1.txt	match zero or one occurrence.
	egrep prashant|director test1.txt	match eap1 or eap2  (finds prashant or line with director)
	egrep (das|sen)gupta test1.txt	match exp x1x3 or x2x3 (like dasgupta & sengupta)
	egrep -f <pattern_file_name> test1.txt	Huge list of pattern search can passed in the form of file name .pattern stored in file eg(prashant|admin|director)
	+	Matches one or more occurrence of previous character.
	?	Matches zero or one occurrence of previous character.
Fgrep		fgrep and egrep accepts multiple pattern both form command line and a file but unlike grep and egrep  does not accept regular expression.
	fgrep -f pattern file emp file	Faster than grep and egrep family