Will discuss about basic regular expression in three stages.

Symbol             Explanation

^                       Start of string
$                       End of string
.                        Any single character
+                       One or more character
                       Escape Special characters
?                       Zero or more characters

Input exactly match with “abc”

Input start with “abc”

Input end with “abc”

Input “abc” and one character allowed Eg. abcx

Input  “abc” and more than one character allowed Eg. abcxy

Input exactly match with “abc.def”, cause (.) escaped

Passes any characters followed or not by “abc” Eg. abcxyz12….

Char                Group Explanation

[abc]                 Should match any single of character
[^abc]               Should not match any single character
[a-zA-Z0-9]      Characters range lowercase a-z, uppercase A-Z and numbers
[a-z-._]              Match against character range lowercase a-z and ._- special chats
(.*?)                  Capture everything enclosed with brackets
(com|info)         Input should be “com” or “info”
{2}                   Exactly two characters
{2,3}                Minimum 2 characters and Maximum 3 characters
{2,}                  More than 2 characters

Put together all in one URL validation.

Short Form     Equivalent              Explanation

d                      [0-9]                         Any numbers
D                     [^0-9]                       Any non-digits
w                     [a-zA-Z0-9_]            Characters,numbers and underscore
W                    [^a-zA-Z0-9_]          Except any characters, numbers and underscore
s                       –                                White space character
S                      –                                Non white space character