sash and msh shells

I'd like to run a not completely initialization script in a µCLinux
system. I can run the "sash" and/or the "msh" shell (sash is the
default, msh can be enabled via busybox).

I need to do some "if" clauses.

Does sash and/or msh provide "if" ? What can be used as decisions ?
(e.g. directory exist, results of commands, ...) What is the syntax ?



I need to use some variables.

I do know that both can do variables, but sash does not have "export".
Are all variables exported by sash, or does it export none ?

I suppose both can do "source" ("." command) to let me set variables
from a file.

Can somebody point me to descriptions of sash and msh ?

Thanks,

-Michael