And this utility made me finally install Go (as packages) for Mac OS X and (Intel based) Linux.
$ .../bin/webp2png -input ___.webp -output ___.png # 'somewhere' on $GOPATH
“go get” is the Go way of installing a package together with its dependencies.
My search for a webp2jpg command line utility wasn’t quite as successful as for webp2png – I am quite glad I found webp2png finally – there a web sites that serve WebP image files only, but I have not utility yet to view such image files.