Regex : referencing an already captured group

Question

I am capturing Bar via a named groupA and I would like to re-reference groupA capture to get a second group.

Sample string :

Foo:Bar Lorem ipsum Bar-564875XC4 dolor sit amet

Regex to capture Bar in groupA :

Foo:(?<groupA>[^\s]+)

Question : how to I complete this regex to re-capture <groupA> and get 564875XC4 in <groupB> ?

What programming language or tool are you using? – Tim Biegeleisen Sep 14 '22 at 23:11 — Tim Biegeleisen, Sep 14 '22 at 23:11

Tim Biegeleisen · Answer 1 · 2022-09-14T23:47:16.770

1

I would write your regex in C# as:

Foo:(?<groupA>\w+)(?: \w+)* \k<groupA>-(?<groupB>\w+)

More generally, you could also just use a numbered backreference:

Foo:(?<groupA>\w+)(?: \w+)* \1-(?<groupB>\w+)

Demo

Explanation:

edited Sep 14 '22 at 23:47

answered Sep 14 '22 at 23:08

Tim Biegeleisen

Can you can use a numbered back-reference to reference a named capture group? – Barmar Sep 14 '22 at 23:09
Numbered back reference will do for my use-case. Any possibility to reference groupA by it's name ? – Philippe Sep 14 '22 at 23:14
What is your regex flavor/language? – Tim Biegeleisen Sep 14 '22 at 23:24
C# but that's not very important. Just found by myself, thanks to your first answer ! – Philippe Sep 14 '22 at 23:26
Check the updated answer for an exact C# regex. – Tim Biegeleisen Sep 14 '22 at 23:47

score 0 · Answer 2 · answered Sep 14 '22 at 23:25

0

Answer with back-reference by name:

Foo:(?<groupA>\w+)(?: \w+)* \g<groupA>-(?<groupB>\w+)

answered Sep 14 '22 at 23:25

Philippe