Re: is (?: ... ) capturing

[ysth]

Capturing refers to data that is put into $1, $2, etc. or returned from a list context m//. You aren't using the result of a capture there, so capturing or not isn't relevant. Even though (?: ) doesn't capture, it does consume part of the string and usually becomes part of what s/// will replace. You can avoid that with a lookbehind instead: s/(?<=\s)\w/_/g. Or, in 5.10+, the \K feature: s/\s\K\w/_/g. See perlre for details.