Regular Expressions Cookbook, 2nd Edition

4.9. Limit the Length of Text

Problem

You want to test whether a string is composed of between 1 and 10 letters from A to Z.

Solution

All the programming languages covered by this book provide a simple, efficient way to check the length of text. For example, JavaScript strings have a length property that holds an integer indicating the string’s length. However, using regular expressions to check text length can be useful in some situations, particularly when length is only one of multiple rules that determine whether the subject text fits the desired pattern. The following regular expression ensures that text is between 1 and 10 characters long, and additionally limits the text to the uppercase letters A–Z. You can modify the regular expression to allow any minimum or maximum text length, or allow characters other than A–Z.

Regular expression

^[A-Z]{1,10}$

Regex options: None

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

Perl example

if ($ARGV[0] =~ /^[A-Z]{1,10}$/) {
    print "Input is valid\n";
} else {
    print "Input is invalid\n";
}

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

Discussion

Here’s the breakdown for this very straightforward regex:

^         # Assert position at the beginning of the string.
[A-Z]     # Match one letter from A to Z
  {1,10}  #   between 1 and 10 times.
$         # Assert position at the end of the string.

Regex options: Free-spacing

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

The ‹^› and ‹$› anchors ensure ...