Find a credit card within a string

Question

I am looking for a way to detect a credit card within a string using C#. Regex is a possibility. I do not want to detect if a string is a credit card.

For example

string text = "Hi mum, here is my credit card 1234-1234-1223-1234. Don't tell anyone";
bool result = TextContainsCreditCard(text);
if (result)
  throw new InvalidOperationException("Don't give people your credit card!");

A sequence of 16+ digits beginning 4/5/6 that pass the luhn (mod10) test — Alex K., Nov 19 '14 at 12:50
Does String.Contains work with a regex? A credit card can be various formats. — Craig, Nov 19 '14 at 12:51
Do you want - as the only number separator, or could it use other symbols? — Kevin Winata, Nov 19 '14 at 12:53
Replace whitespace/- use a regex to capture ([456]\d{16,25}), test matches with luhn — Alex K., Nov 19 '14 at 12:54
I think potentially spaces or - could also be separator. This is a free text field. — Craig, Nov 19 '14 at 12:54
Is this helpful for you: http://stackoverflow.com/questions/72768/how-do-you-detect-credit-card-type-based-on-number ? — Shaharyar, Nov 19 '14 at 12:58
Make a list of all credit card formats you want to check against. Make a regex for each format. Possibly combine regexes. Check string against all of them. Perform additional tests (luhn). — Corak, Nov 19 '14 at 12:58
http://stackoverflow.com/questions/1463252/creditcard-verification-with-regex — , Nov 19 '14 at 13:11

score 6 · Accepted Answer · answered Nov 19 '14 at 13:00

6

You can use regex like

(\d{4}[\s-]?){4}

And put any chars you want as separator to [\s-] now they are only space and minus

And this allows separators in any position (\d[\s-]?){16} like 1 2341234-12341 234

answered Nov 19 '14 at 13:00

Pavel Krymets

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score 1 · Answer 2 · answered Nov 19 '14 at 12:58

1

Well, if your separator is ONLY spaces or -, then the regex to detect the credit card would be

([0-9]{4}(-| )){3}[0-9]{4}

or maybe there are shorter or better options.

answered Nov 19 '14 at 12:58

Kevin Winata

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score 0 · Answer 3 · answered Nov 19 '14 at 12:56

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I have drafted this algorithm (would place as comment only it would be badly formatted)

Split string on (-)
See if string contains numeric values.
See if there are 4+ parts
See if parts[0] + parts[1] (i.e. four in a row)
If so, return true, if not, return false?

answered Nov 19 '14 at 12:56

jbutler483

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Presumably not everyone will neatly delimit their card numbers – Alex K. Nov 19 '14 at 12:56
I'm not great with implementation, but @AlexK. I think checking if there are 16 digits, and ensuring that they form a credit card, is pretty difficult to master a 'perfect' algorithm. – jbutler483 Nov 19 '14 at 13:01

score 0 · Answer 4 · answered Nov 19 '14 at 13:41

0

You can use the below regex to do it

(\d{4}-?){4}

Here is the sample output with grep.

$ echo "Hi mum, here is my credit card 1234-1234-1223-1234. Don't tell anyone"|grep -Po "(\d{4}-?){4}"
1234-1234-1223-1234

answered Nov 19 '14 at 13:41

Kannan Mohan

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Find a credit card within a string

4 Answers4