Regex patterns for AANNN and ANEE formats

Question

I need regex patterns for the AANNN and ANEE formats.

• A means letters
• N means digits
• E means either letters or digits.

I need to validate input strings according to these formats.

Examples

• BD123 matches the AANNN
• G21H matches the ANEE

Answer 1

I'm assuming you want ASCII letters and digits, but not Thai digits, Arabic letters and the like.

1. AANNN is (?i)^[a-z]{2}[0-9]{3}$
2. ANEE is (?i)^[a-z][0-9][a-z0-9]{2}$

Explanation

• The ^ anchor asserts that we are at the beginning of the string
• [a-z] is what's called a character class. It allows any chars between a and z.
• In a character class we can include several ranges, that's why the E is [a-z0-9]
• Normally for A you would have to say something like [a-zA-Z], but the (?i) flag makes it case-insensitive
• {2} is a quantifier that means "match the previous expression twice
• The $ anchor asserts that we are at the end of the string

How to Use

In Java, you can do something like:

if (subjectString.matches("(?i)^[a-z]{2}[0-9]{3}$")) {
    // It matched!
    } 
else {  // nah, it didn't match...  } 

Regular Expressions are Fun! I highly recommend you go learn from one of these resources.

Resources

• Regex FAQ on Stack Overflow.
• Character Classes
• Mastering Regular Expressions, 3rd Ed
• The Regular Expressions Cookbook, 2nd Ed