Regular Expressions 101

Explanation

Pro

Comment: This regex was created for the purposes of detecting potentially compromised credentials for the purposes of information security and not to be used for malicious purposes.

Negative Lookbehind(?<!\d)

\da digit

Comment: s - Short [less than 16 digits], m - Medium [16 digits], l - Long [more than 16 digits; not yet implemented]

Comment: First four digits

Non-Capturing Group(?: (?# Standard 16 digit numbers) (?<m> (?#MasterCard between 222100-272099) 222[1-9]|223\d|2[3-6]\d{2}|27[01]\d|2720| (?#JCB is between 3528-3589) 352[89]|35[3-8]\d| (?#Visa, MasterCard, Discover) [4-6]\d{3} )| (?#American Express 15 digits | Diners Club 14 digits) (?<s>(?<ax>3[47]\d{2})|(?<dc>30[0-5]\d|36\d{2})) )

1st Alternative (?# Standard 16 digit numbers) (?<m> (?#MasterCard between 222100-272099) 222[1-9]|223\d|2[3-6]\d{2}|27[01]\d|2720| (?#JCB is between 3528-3589) 352[89]|35[3-8]\d| (?#Visa, MasterCard, Discover) [4-6]\d{3} )

Comment: Standard 16 digit numbers

Group m(?<m> (?#MasterCard between 222100-272099) 222[1-9]|223\d|2[3-6]\d{2}|27[01]\d|2720| (?#JCB is between 3528-3589) 352[89]|35[3-8]\d| (?#Visa, MasterCard, Discover) [4-6]\d{3} )

1st Alternative (?#MasterCard between 222100-272099) 222[1-9]

Comment: MasterCard between 222100-272099

222the literal text 222

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

2nd Alternative223\d

223the literal text 223

\da digit

3rd Alternative2[3-6]\d{2}

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Character Class[3-6]

3-6one character from 3 (51₁₀) to 6 (54₁₀)

\d{2}a digit, repeated exactly 2 times

4th Alternative27[01]\d

27the literal text 27

Character Class[01]

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

\da digit

5th Alternative2720

2720the literal text 2720

6th Alternative (?#JCB is between 3528-3589) 352[89]

Comment: JCB is between 3528-3589

352the literal text 352

Character Class[89]

8the literal 8 (56₁₀ / 70₈ / 38₁₆)

9the literal 9 (57₁₀ / 71₈ / 39₁₆)

7th Alternative35[3-8]\d

35the literal text 35

Character Class[3-8]

3-8one character from 3 (51₁₀) to 8 (56₁₀)

\da digit

8th Alternative (?#Visa, MasterCard, Discover) [4-6]\d{3}

Comment: Visa, MasterCard, Discover

Character Class[4-6]

4-6one character from 4 (52₁₀) to 6 (54₁₀)

\d{3}a digit, repeated exactly 3 times

2nd Alternative (?#American Express 15 digits | Diners Club 14 digits) (?<s>(?<ax>3[47]\d{2})|(?<dc>30[0-5]\d|36\d{2}))

Comment: American Express 15 digits | Diners Club 14 digits

Group s(?<s>(?<ax>3[47]\d{2})|(?<dc>30[0-5]\d|36\d{2}))

1st Alternative(?<ax>3[47]\d{2})

Group ax(?<ax>3[47]\d{2})

3the literal 3 (51₁₀ / 63₈ / 33₁₆)

Character Class[47]

4the literal 4 (52₁₀ / 64₈ / 34₁₆)

7the literal 7 (55₁₀ / 67₈ / 37₁₆)

\d{2}a digit, repeated exactly 2 times

2nd Alternative(?<dc>30[0-5]\d|36\d{2})

Group dc(?<dc>30[0-5]\d|36\d{2})

1st Alternative30[0-5]\d

2nd Alternative36\d{2}

Comment: Rest of the card number

Group del(?<del>\D+)?

Condition(?(<m>)\d{4}(?(<del>)\k{del})\d{4}(?(<del>)\k{del})\d{4}|(?:\d{6})(?(<del>)\k{del})(?(<ax>)\d{5}|\d{4}))

Comment: END

Negative Lookahead(?!\d)

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

x modifier: extended. Ignores unescaped whitespace and comments outside character classes

Unit Test Summary

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Quick Reference

25 tokens

Regular Expression

(?# This regex was created for the purposes of detecting potentially compromised credentials for the purposes of information security and not to be used for malicious purposes.)
(?<!\d)
(?# s - Short [less than 16 digits], m - Medium [16 digits], l - Long [more than 16 digits; not yet implemented])
(?# First four digits)
(?:
  (?# Standard 16 digit numbers)
  (?<m>
    (?#MasterCard between 222100-272099)
    222[1-9]|223\d|2[3-6]\d{2}|27[01]\d|2720|
    (?#JCB is between 3528-3589)
    352[89]|35[3-8]\d|
    (?#Visa, MasterCard, Discover)
    [4-6]\d{3}
  )|
  (?#American Express 15 digits | Diners Club 14 digits)
  (?<s>(?<ax>3[47]\d{2})|(?<dc>30[0-5]\d|36\d{2}))
)
(?# Rest of the card number)
(?<del>\D+)?(?(<m>)\d{4}(?(<del>)\k{del})\d{4}(?(<del>)\k{del})\d{4}|(?:\d{6})(?(<del>)\k{del})(?(<ax>)\d{5}|\d{4}))
(?#END)
(?!\d)

Unit Tests

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