You can use any separator you want in an s/../../ expression, not just /, in this case the separator is _ (this technique allows you to use / without creating a

You can use any separator you want in an s/../../ expression, not just /, in this case the separator is _ (this technique allows you to use / without creating a "picket fence": s/r\/x/r$\//). So the regex just means replace "r/x" with "r$/".