Some people like to put - or space between subgroups of digits when writing their credit card number, hence the above REs would fail to capture them.
Can you please dissect the RE:
(?:\d[ -]*?){13,16}\b
and explain why it can solve the problem?
I know *? will match the previous element zero or more times, but as few times as possible.
(?:some regex) indicate non capturing group
\d indicate decimal is exepted such as [0-9]
[] indicate to match any character in this.
In fact [ -] indicate to find space or -
* indicate 0 or more
{} is a range of repetition with (xMin, xMax)
{13, 16} => Repeted 13 or more but less than 17
\b indicate the pattern must terminated by presceding token.
For this question \b refer to the non capturing group
You can try the behavior of this regex on http://regexr.com/.
Some valid pattern are:
0332 - 221 - 212 - 111
0-11 -0151- 0151 - 10
0000 - 0000 - 0000 - 0
0000 - 0000 - 0000 - 00
0000 - 0000 - 0000 - 000
0000 - 0000 - 0000 - 0000
00000 - 0000 - 0000
0000-0000-0000-0000
0-0-0-0-0-0-0-0-00-0-0-0
First of all, Capturing Groups are used to groups parts of the RegEx. They are defined by putting () around the data you want in the group. A Non-Capturing Group is defined by adding ?: inside the (), like so, (?:data)
Secondly, a Lazy RegEx is one that tries to capture as little as possible, rather than as much as possible. Check out this StackOverflow question
How the RegEx works:
(?: # Non-Capturing Group
\d # Digit
[ -]*? # Space or - (Hyphen), 0 or more times (Lazy)
)
{13,16} # Repeats the Non-Capturing Group 13 to 16 times
\b # Word Boundary
The Non-Capturing Group will match any string containing 1 Digit, combined with any number of Space (spaces) and - (hyphens). So 9, -9-, - 9 -, 9 and - - - 9 - - - are all matches.
Then the group can be repeated 13 to 16 times, so the examples above can be repeated 13 to 16 times, to match each Credit Card Digit
So these are all full valid matches:
9999 - 9999 - 9999 - 9
9999 - 9999 - 9999 - 99
9999 - 9999 - 9999 - 999
9999 - 9999 - 9999 - 9999
999 - 999 - 999 - 999 - 999
99-99-99-99-99-99-99
9-9-9-9-9-9-9-9-9-9-9-9-9
\d matches a digit (Does "\d" in regex mean a digit?)
\b marks the end of a word/number
[0-9]{13-16} indicates that the repetition of the characters in the brackets before, either 13,14,15 or 16 times. The background is that old credit cards numbers have 13 digits newer credit card numbers have 16 digits.
So \b\d{13,16}\b will find/match any sequence of 13 to 16 digits, meaning that it can be used to find credit card numbers without any '-'
?: is another special case meaning 'clustering without capturing` (use of colon symbol in regular expression)
(?:pattern) is used to match the pattern, but not capture it resulting in removing the questioned characters from the result string, i.e. the '-' (What is a non-capturing group? What does a question mark followed by a colon (?:) mean?)
* means zero or more repetitions of the character(s) in the element before
? means the characters in the element before can appear, but don't have to
*? (used in the regex above) is the non-greedy / lazy version i.e. [^a]*? means "a sequence of 0 or more characters, not containing 'a', as short as possible while conforming to the rest of the regular expression."
So the regex matches any sequence of numbers of length 13 to 16 containing an arbitrarily number of '-' and ' ' (whitespaces)
Note that the non-capturing group ?: matches but does not capture the substring in the result: The regex \b(a)(?:b)(c)\b applied on the string "abc" matches but in the result the non-capturing group is skipped ( a group is everything in ( )):
match: "abc", match1: "a", match2: "c" ("b" does not appear in the match list)
However the entire match can be retrieved by calling group() on the match object, see Alan Moore's comment below.
You can test this on https://regex101.com/
See this Regex credit card number tests
