What does .* do in regex?

Question

After extensive search, I am unable to find an explanation for the need to use .* in regex. For example, MSDN suggests a password regex of

@\"(?=.{6,})(?=(.*\d){1,})(?=(.*\W){1,})"

for length >= 6, 1+ digit and 1+ special character.

Why can't I just use:

@\"(?=.{6,})(?=(\d){1,})(?=(\W){1,})"

Answer 1

.* just means "0 or more of any character"

It's broken down into two parts:

• . - a "dot" indicates any character
• * - means "0 or more instances of the preceding regex token"

In your example above, this is important, since they want to force the password to contain a special character and a number, while still allowing all other characters. If you used \d instead of .*, for example, then that would restrict that portion of the regex to only match decimal characters (\d is shorthand for [0-9], meaning any decimal). Similarly, \W instead of .*\W would cause that portion to only match non-word characters.

A good reference containing many of these tokens for .NET can be found on the MSDN here: Regular Expression Language - Quick Reference

Also, if you're really looking to delve into regex, take a look at http://www.regular-expressions.info/. While it can sometimes be difficult to find what you're looking for on that site, it's one of the most complete and begginner-friendly regex references I've seen online.