Regular Expressions in VBScript - Building useful patterns
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Now that you have all of the tools, let’s look at how to make them work. Say we wanted to build a regular expression to match a standard ten-digit phone number in the form of (xxx) xxx-xxxx.
The regular expression could easily begin as “(ddd) ddd-dddd”. This is a string of literals: an opening parenthesis followed by three digits, a closing parenthesis, a space, three more digits, a hyphen, and the last four digits.
If we apply repetition, we can condense this a bit to “(d{3}) d{3}-d{4}”. Both expressions mean the same thing. Now what if we wanted to make the parentheses optional? Of course, if we do, the space should be a hyphen. Enter grouping and alternation.
To begin, we need to specify what it should look like with parentheses. Thus our expression should begin with “(d{3) ” as before. Now we want to add an alternate possibility in case parentheses aren’t used. The expression then becomes “((d{3))|(d{3}-)”. This will match three digits between parentheses followed by a space, OR three digits followed by a hyphen. We then complete the expression by adding the remaining part of the match. The final expression looks like “((d{3))|(d{3}-)d{3}-d{4}”. This expression would match either “(123) 456-7890” or “123-456-7890.
Another example would be a common U.S. zip code. A U.S. zip code consists of five numeric digits followed by an optional four more separated by a hyphen. Just as in the previous example, you can use grouping to accomplish this quite easily. That expression would look like “d{5}(-d{4})?”. Notice this time that I’m using the ? symbol to match either 0 or 1 of the last group.
You can see that building regular expressions can provide very powerful tools for matching and replacing text strings. Very complex expressions can be built using a simple set of character symbols. Stayed tuned for a future article that demonstrates more advance uses of VBScript regular expressions.
If you’re interested in testing your regular expressions, I’ve built a Regular Expression Tester HTML application using the regular expression test code found here. Until next time, keep coding!
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