AND operator in regular expression?

Question

Given a string, how do I express that a pattern must match multiple regex using the AND operator? For example, I want a password to be a minimum of 5 characters AND maximum of 12 characters.

• Regex for mimimum 5 characters: .{5,}
• Regex for maximum 12 characters: .{12}

I know I can combine the above two to something like this: .{5,12}, but this is not what I am trying to achieve. I want to "and" the two regexes.

Answer 1

The two source regexes are wrong. Anyways, you want .{5,12}.

Answer 2

If you want to check multiple pattern on a string, you can use a look-around :

/^(?=.{5}).{0,12}$/

This way you check that your string is at least 5 chars, and is also at most 12 chars.

But as you said, in this case it's better to combine the two of them in .{5,12}.

Answer 3

Well 99% of the time, you would either want to combine them in the parent language, eg.

if (Regex.Match(input,pattern1) && Regex.Match(input,pattern2))
{
   //do work
}

or improve the regex to combine them, eg.

.{5,12}

If you really want to combine within a single regex, you can use look ahead assertions, something like this, but the actual matched value will not be what you might expect.

^(?=.{5,})(?=.{0,12})

Answer 4

There is no simple way to do this within the regexes themselves. The algorithms for regex intersection that I know require that you first convert the regex to an automaton.

In your case, the best solution would probably be to create an AndRegex class which combines two regexes.

Answer 5

If you just want to match min of 5 chars and max of 12, why even bother with regex? You can just use whatever functions your language supports for counting number of characters in a string. Eg Python using len()

>>> s="mypassword"
>>> if len(s) >=5 and len(s) <=12 :
...   print s
...
mypassword

With Ruby

>> s="mypassword"
=> "mypassword"
>> s.size >= 5 and s.size<=12
=> true