The previous replies were all too pretty...

perl -wE '$_ = "7-12"; say join " ", [/(\d+)-/]->[0]..[/-(\d+)/]->[0]'
[download]

:-)

Update: slightly less ugly?

perl -wE '$_ = "7-12"; say join " ", (/(\d+)-/)[0]..(/-(\d+)/)[0]'
[download]