You can use them to constrain input, apply formatting rules, and check lengths. By using capturing groups to remember each set of digits, the same regular expression can be used to replace the subject text with precisely the format you want.
Regex class for validate any input string for any specific format.
These rules are quite easy to understand and are listed on the number format page and detailed in the Reg Ex patterns in section 3 of this article. You can choose to display the number in national format, e.g. The following Reg Ex patterns select valid GB telephone number ranges: Note: These are a subset of the fixed-line rules, with digits 2 to 9 as the leading digit of the subscriber number.
Any of the previous two options are then followed by 44 with optional closing parentheses, followed by optional space or hyphen, followed by optional 0 in optional parentheses, followed by optional space or hyphen, followed by optional opening parentheses (international format).
Alternatively, the initial opening parentheses are followed by a literal without a following space or hyphen. Note: These area codes are very rare in GB, and are only available in the following places: 13873 (Langholm), 15242 (Hornby-with-Farleton), 15394 (Hawkshead), 15395 (Grange-over-Sands), 15396 (Sedbergh), 16973 (Wigton), 16974 (Raughton Head), 16977 (Brampton), 17683 (Appleby-in-Westmorland), 17684 (Pooley Bridge), 17687 (Keswick), 19467 (Gosforth).
Do a few basic checks on the prefix and length and then remove the 44 country code or 0 trunk code and any extension details from the number and store for later use.
Next, remove all punctuation and spaces from the remainder so that you're left with the 7, 9 or 10 digit National Significant Number.