Regular Expressions Cookbook, 2nd Edition

4.14. Validate ZIP Codes

Problem

You need to validate a ZIP code (U.S. postal code), allowing both the five-digit and nine-digit (called ZIP+4) formats. The regex should match 12345 and 12345-6789, but not 1234, 123456, 123456789, or 1234-56789.

Solution

Regular expression

^[0-9]{5}(?:-[0-9]{4})?$

Regex options: None

Regex flavors: .NET, Java, JavaScript, PCRE, Perl, Python, Ruby

VB.NET example

If Regex.IsMatch(subjectString, "^[0-9]{5}(?:-[0-9]{4})?$") Then
    Console.WriteLine("Valid ZIP code")
Else
    Console.WriteLine("Invalid ZIP code")
End If

See Recipe 3.6 for help with implementing this regular expression with other programming languages.

Discussion

A breakdown of the ZIP code regular expression follows:

^           # Assert position at the beginning of the string.
[0-9]{5}    # Match a digit, exactly five times.
(?:         # Group but don't capture:
  -         #   Match a literal "-".
  [0-9]{4}  #   Match a digit, exactly four times.
)           # End the noncapturing group.
  ?         #   Make the group optional.
$           # Assert position at the end of the string.

Regex options: Free-spacing

Regex flavors: .NET, Java, XRegExp, PCRE, Perl, Python, Ruby

This regex is pretty straightforward, so there isn’t much to add. A simple change that would allow you to find ZIP codes within a longer input string is to replace the ‹^› and ‹$› anchors with word boundaries, so you end up with ‹\b[0-9]{5}(?:-[0-9]{4})?\b›.

Tip

There is one valid ZIP+4 code that this regex will not match: 10022-SHOE. This is the only ZIP code that includes letters. In 2007, it was assigned ...