regular expression with the same element twice without knowing it

Question

I've plenty fill and want to find all of them which are like this:

A = A + B

So I wanna use a regular expression using M + x rgrep. and was thinking to something like that: ([A-Za-z][A-Za-z0-9]*) = () + [A-Za-z][A-Za-z0-9]* where () create a group which can be used latter.

Their is a way to make a regular expression where two item must be the same but without knowing the form of them?

Avinash Raj · Accepted Answer · 2014-07-07T12:08:09.337

1

I think you want something like this,

([A-Za-z][A-Za-z0-9]*) = \1 \+ [A-Za-z][A-Za-z0-9]*

DEMO

edited Jul 07 '14 at 12:08

answered Jul 07 '14 at 12:02

Avinash Raj

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It's the behavior I want. But when I try it with emacs or in tty, I have an error: `grep: invalid back reference` – Romain Picot Jul 07 '14 at 12:10
Back reference may differ for languages. It would be `\1` or `$1` or `#1` – Avinash Raj Jul 07 '14 at 12:11
For grep it's $1. Perfect. Thank you `:)` – Romain Picot Jul 07 '14 at 12:13

regular expression with the same element twice without knowing it

1 Answers1