Repeating pattern for a regex -- validate the same

Question

The url of my username is:

https://stackoverflow.com/users/12283851/user12283851

For this username it looks like the regular expression might be close to:

r'https?://stackoverflow.com/users/\d{1,9}/user\d{1,9}'

Is there a way in the regex to make sure that the first ID matches the second? In other words:

https://stackoverflow.com/users/12283851/user12283851 <== Valid
https://stackoverflow.com/users/11111111/user12283851 <== Invalid

You could use a backreference `https?://stackoverflow\.com/users/(\d{1,9})/user\1` See https://regex101.com/r/PWGEDN/1/ — The fourth bird, Oct 28 '19 at 21:09

Pedro Pinheiro · Accepted Answer · 2019-10-29T11:36:02.677

0

This is accomplished by using backreferences.

The backreference \1 (backslash one) references the first capturing group. \1 matches the exact same text that was matched by the first capturing group

In your example the following regex would work:

https?://stackoverflow\.com/users/(\d{1,9})/user\1

See this demo

edited Oct 29 '19 at 11:36

answered Oct 28 '19 at 21:15

Pedro Pinheiro

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You don't have to escape the backslashes. – The fourth bird Oct 28 '19 at 21:17
You are right, I updated the answer. I was used to escape the backslashes because it is the default delimeter on regex101. Thanks! – Pedro Pinheiro Oct 29 '19 at 11:37

Repeating pattern for a regex -- validate the same

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