Ruby String: how to match a Regexp from a defined position

Question

I want to match a regexp from a ruby string only from a defined position. Matches before that position do not interest me. Moreover, I'd like \\A to match this position.

I found this solution:

code[index..-1][/\A[a-z_][a-zA-Z0-9_]*/]

This match the regexp at position index in the string code . If the match is not exactly at position index , it return nil .

Is there a more elegant way to do this (I want to avoid to create the temporary string with the first slice)?

Thanks

Answer 1

You could use ^.{#{index}} inside the regular expression. Don't know if that's what you want, because I don't understand your question completely. Can you maybe add an example with the tested String? And have you heard of Rubular ? Great way to test your regular expressions.

This is how you could do it if I understand your question correctly:

code.match(/^.{#{index}}your_regex_here/)

The index variable will be put inside your regular expression. When index = 4 , it will check if there's 4 characters from the beginning. Then it will check your own regular expression and only return true if yours is valid as well. I hope it helps. Good luck.

EDIT

And if you want to get the matched value for your regular expression:

code.scan(/^.{#{index}}([a-z_][a-zA-Z0-9_]*)/).join

It puts the matched result (inside the brackets) in an Array and joins it into a String.