Tag Archive Regular Expressions

ByMel

Credit Card Regular Expression

So for the project I’m currently working on I need to verify credit card numbers input by the user. So I found a regular expression online that would do almost all of it, but it lacked a few necessary validations such as Discover cards and 13-digit Visas. So I modified it to work with almost all forms of Visa, MasterCard, American Express, and Discover cards.

It also supports white space and dashes in between blocks of numbers, as would be found on an actual credit card.

Here it is:

^(((4\d{3})|(5[1-5]\d{2})|(6011))[-\s]?\d{4}[-\s]?\d{4}[-\s]?\d{4})|(3[4,7][\d\s-]{13})|(4[\d\s-]{12})$

It’s not 100% perfect for catching invalid Discover or 13-digit Visa cards but it will recognize valid ones. For best results, strip out any non-digits from the input string before running it through the regular expression.

Cheers!

ByMel

C#: Retrieve data from webpage

So I came across a fun assignment this week that I’m sure has been done by many different people in many different programming languages. The challenge was to “scrape” a website for information autonomously and save it off to a file.

I accomplished this by first using a wrapper class for .NET’s own HTTPWebRequest object that simplified posting to a web site and retrieving the result. I then used regular expressions to find the data I wanted, stored it in a string, and later wrote it to a file.

I’m not going provide the specific program I wrote as it’s still proprietary, but I will give a small example of how this can be done. The example will include: posting to a website, retrieving the results (HTML for the page), and parsing the resulting page to find what you want.

The class I used to post to the site was done by Robert May and can be found here: http://geekswithblogs.net/rakker/archive/2006/04/21/76044.aspx

Here is an example of using this class to perform a search at CraigsList under the ‘for sale’ category and retrieving the results:

// Create the post object
PostSubmitter post =
    new PostSubmitter("http://provo.craigslist.org/search/sss");

// Add our parameters
post.PostItems.Add(
    "query",
    "Ford Truck"
);

// Specify our action type (Post | Get)
post.Type = PostSubmitter.PostTypeEnum.Get;

// Retrieve the results
string result = post.Post();
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ByMel

C#: Regular Expressions

I’ve decided to document what little knowledge I have on using Regular Expressions in C#. Nothing grand, just a list of formats, special characters and usage.

Control Characters:

Character Matches
. Any character but the newline (\n)
$ Characters at the end of a string
^ Characters at the beginning of a string. Also used in conjunction with ‘[]’ to specify “not.”
+ One or more of the specified characters
* Zero or more of the specified characters
? Zero or One of the specified characters
\ Used to escape special characters as well as signify special character sets
( ) Used to specify a collection of characters to match
[ ] Used to specify a set of single characters or ranges to match
{ } Used to specify how many times to match a given character(s)
| Used as a logical OR. Allows one or more expressions to be selected for a match

Special Character Sets:

Character Matches
\w Any word character. Same as [A-Za-z0-9_]
\W Any non-word character. Same as [^A-Za-z0-9_]
\s Any whitespace character. Same as [ \t\v]
\S Any non-whitespace character. Same as [^ \t\v]
\d Any digit. Same as [0-9]
\D Any non digit. Same as [^0-9]

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