Exact n times repetition quantifier {n}

Q

What is the exact n times repetition quantifier? How to use it?

How to write a regular expression using a repetition quantifier to capture Visa card numbers that have 16 digits like this: 4111111111111111?

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A

The "exact n times" repetition quantifier allows us to repeat a pattern unit exactly n times in the matching process. The "exact n times" repetition quantifier is '{n}' and it needs be placed immediately after the pattern unit. For example:

\d{2}-\d{2}-\d{4}   # matches date strings in mm-dd-yyyy format

The regular expression to capture 16-digit Visa card numbers is:

4\d{15}

4 - matches '4', the starting digit of all Visa numbers
\d{15} - repeating \d exactly 15 times

Click the button to test this regular expression here online:

2013-01-26, 2108👍, 0💬