search textfiles with regular expressions

regular express

--grep,
--fgrep,
--egrep
--regex


grep search through stream

syntax
grep [string to find] [file name]

grep -n[string to find] ] [filename]

grep is case sensitive to make case insensitive add -i flag
regular expressions inside the grep
^ ==  means == starts with              grep ^boo file.txt  ==  list all the lines with boo starting 
$ ==  means == ends with                grep oks$ file.txt  ==  list all the lines with oks ending
. ==  means == any single character     grep .oo file.txt   ==  list all the lines with any character start but                                                                 oo next characters


egrep: grep with more regular expression

egrep '^(b|d)' file.txt     search all the words that starts with either b or d
egrep '(b|d)oo' file.txt    search all the words that starts with b or d and followed by oo


fgrep dosent support any kind of regular expresstion


man regex command for more information