[greggyb]

Osh is stricter than bash. Anything written to osh should run in bash with no issues whatsoever.

Ysh implements new, non-compatible syntax and semantics.

Osh and ysh are two different shell languages from the Oils for UNIX project. The release build generates a single binary, oils-for-unix, and installation creates two symlinks for the two different shell personalities, similar to how the bash binary will behave in its POSIX-compliant mode when it is invoked as sh.

There is no "Oil shell" now, at least not without ambiguity.