Regular Expression

				^ caret ^aaa	the first line or beginning of string in the beginning of string, if there is "aaa" then true,otherwise false
				$ dollar aaa$	end of line or end of string in the end of line, if the line end with "aaa", then true, otherwise false
				. period ^a.c a..b$	exact one character "abc","adc","aZc",.. are true, "aa" is false end of string with these string,"aaab","abbb",azzb",..., then true
				[] bracket [^xxxx] [:string class:] [:digit:] [:alpha:] [abc] [Yy] [A-Za-z0-9] [-A-Z] [^a-z] [^0-9] [[:digit:]]	means reange or group, between two character use "-" ^ inside of [], means not string class, alpha, blank,cntrl, digit,graph,lower,print,space,upper,xdigit same with [0-9] same with [A-Za-z] same with [a-c]. so, "a","b","c" one of these are true Y or y is true all alphabet and numbers with hyphen and all capital except lowercase, all string except number, all string same with [0-9]
				{} brace a{3} a{3,} a{3,5} ab{2,3} [0-9]{2} doc[7-9]{2} [^Zz]{5} .{3,4}er	{} means range or repeat for right before the character repeat 'a' only, so only "aaa" is true 'a' repeat more than three, so "aaa","aaaa","aaaaa",... are true only "aaa","aaaa","aaaaa" are true only "abb","abbb" are true two digit number "doc77","doc87","doc97" ...., are true without Z and z, five character, "abcde", "ttttt"..., are true before "er" needs three or four character, Peter,mother, but not brother
				* asterisk ab*c * .* ab* a* doc[7-9]* [A-Z].* like.*	means right before character does appear 0 or more, same as {0,} "ac", "ackdddd", "abc", "abbc", "abbbbbbbc" , etc are true there is no previous character, some characters or space are true "." means one more character, so one more characters or space are not true "b" can repeat 0 or mroe, so 'a', "accc", "abb", "abbbbbbb" are true 'a' repeat 0 or more, so k, kdd, sdfrrt, a, aaaa, abb, space, ... doc7,doc777,doc778989,doc,... are true the string are composed with only capital previous character is 'a', so like, likely, liker, likelihood...are true
				+  plus ab+c ab+ like.+ [A-Z]+	previous a character repeats one or more like {1,} abc, abckdddd, abbc, abbbbbbbc ....are true, but not ac repeat 'b' one or more, so " ab", "abccc", "abb", "abbbbbbb"..., after "like" one character and one or more, "likely", liker, likelihood..., but not "like" capital string
				? question ab?c	previous a character repeat 0 or one only "abc", "abcd" are true
				() parenthesis	it used for group in regular expression
				| bar a|b|c yes|Yes korea|japan|chinese	means or same as [a-c] means one of 'a','b','c' same as [yY]es one of "korea","japan","chinese"
				\ backslash	use to display special character in the string

from : http://ttongfly.net/zbxe/?document_srl=43635