Ruby Regexp gsub, replace instances of second matching character

Question

I would like to replace the first letter after a hyphen in a string with a capitalised letter.

"this-is-a-string" should become "thisIsAString"

"this-is-a-string".gsub( /[-]\w/, '\1'.upcase ) 

I was hoping that \\1 would reinsert my second character match \\w and that I could capitalise it.

How does one use the \\0 \\1 etc options?

Answer 1

You need to capture \\w to be able to refer to the submatch.

Use

"this-is-a-string".gsub(/-(\w)/) {$~[1].upcase}
# => thisIsAString

See the Ruby demo

Note that $~[1] inside the {$~[1].upcase} block is actually the text captured with (\\w) , the $~ is a matchdata object instantiated with gsub and [1] is the index of the first group defined with a pair of unescaped parentheses.

See more details about capturing groups in the Use Parentheses for Grouping and Capturing section at regular-expressions.info.