piranha/goreplace — pull request #19 by tcard (2013-12-17 14:57:40+00:00)
Title: Match placeholders in the replacement string with matched subgroups.

`goreplace '(Happy) (Christmas|Xmas)' -r '$1 ☃☃ $2 ☃☃'`

So `Happy Christmas` turns into `Happy ☃☃ Christmas ☃☃`.

(There's a bunch of changes made by `go fmt`, I hope you don't care.)