Regular expressions are a language of their own. When you learn a new programming language, they're this little sub-language that makes no sense at first glance. Many times you have to read another tutorial, article, or book just to understand the "simple" pattern described.
In computing, regular expressions provide a concise and flexible means for identifying strings of text of interest, such as particular characters, words, or patterns of characters.
Here are some of the most useful Regular expressions Patterns.
- Username
Pattern:
/^[a-z0-9_-]{3,16}$/Description:
We begin by telling the parser to find the beginning of the string (^), followed by any lowercase letter (a-z), number (0-9), an underscore, or a hyphen. Next, {3,16} makes sure that are at least 3 of those characters, but no more than 16. Finally, we want the end of the string ($).
String that matches:
my-us3r_n4m3
String that doesn't match:
th1s1s-wayt00_l0ngt0beausername (too long)
- Password
Pattern:
/^[a-z0-9_-]{6,18}$/Description:
Matching a password is very similar to matching a username. The only difference is that instead of 3 to 16 letters, numbers, underscores, or hyphens, we want 6 to 18 of them ({6,18}).
String that matches:
myp4ssw0rd
String that doesn't match:
mypa$$w0rd (contains a dollar sign)
Pattern:
/^([a-z0-9_\.-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$/Description:
We begin by telling the parser to find the beginning of the string (^). Inside the first group, we match one or more lowercase letters, numbers, underscores, dots, or hyphens. I have escaped the dot because a non-escaped dot means any character. Directly after that, there must be an at sign. Next is the domain name which must be: one or more lowercase letters, numbers, underscores, dots, or hyphens. Then another (escaped) dot, with the extension being two to six letters or dots. I have 2 to 6 because of the country specific TLD's (.ny.us or .co.uk). Finally, we want the end of the string ($).
String that matches:
john@doe.com
String that doesn't match:
john@doe.something (TLD is too long)
More reading\testing at:
- regexlib.com
- supercrumbly.com
- txt2re.com
