Start of string anchor ^

Q

What is the "start of string" anchor in a regular expression? How to use it?

How to write a regular expression using "start of string" anchor to validate discover credit card numbers like: 6011963280099774?

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A

The "start of string" anchor is an atomic zero-width assertion specifing that the match must occur at the beginning of the string. The "start of string" anchor is represented as '^'. For example:

^5\d*   # matches MasterCard numbers starting with '5'

The regular expression to validate Discover credit card numbers:

^6011\d{12}

^ - matches 'start of string'
\d{12} - repeats \d 12 times

Click the button to test this regular expression here online:

2013-01-26, 2064👍, 0💬