It is indeed copied from some other Scheme, though I can't recall which. Rather embarrassingly, I've never fired up Scheme48, or used the original scsh.
Lots of the POSIX bits in Guile were inspired by scsh though, originally anyway. Most of those pieces are 10+ years old.
There are ports around for scsh; googling "guile scsh" will lead you to a few. But there is no proper package with a proper manual.
Scsh: There was a whole lot of noise and some code about supporting Scsh on Guile early last decade, as there was for PLT Scheme, but both seem to have run out of steam. I think that replicating Scsh is harder than it looked at first.
I'm really pleased to see the work on the command language and bytecode interpreter. Scsh is something I've built a few times, but never got into. First the sounds of progress on the Emacs/guile front and now this look positive: it's a good time to take another look at Guile.
Lots of the POSIX bits in Guile were inspired by scsh though, originally anyway. Most of those pieces are 10+ years old.
There are ports around for scsh; googling "guile scsh" will lead you to a few. But there is no proper package with a proper manual.