DASH vs J

Dash has a very fast startup, this happens because the shell is started a lot of times during boot and dash minimizes the work it does during this process.

It is designed to be very lightweight and has no support for shell specific extensions that are not POSIX.

DASH is the default shell for Debian based systems due to it speed, full POSIX compliance and low overhead.

It's fully POSIX compatible, so if your script runs on dash it will probably run on all other shells.

It's a clone of the original System V4 Bourne shell.

3 classes of operators (verbs, adverbs, and conjunctions) with verbs the most basic function that take either 1 or 2 (infix) parameters. Operators allow function composition with a minimum of parentheses.

J also supports multiline functional definitions similar to BASIC/Pascal. Including error handling.

Each built in operator is a C/asm function, and special code further optimizes some operator combinations. Result is optimized C speed from quick parsing. Array orientation parses and compiles a function once, and applies it to all array items.

Still actively developed, but most recent changes have been in libraries and IDE and platform support.
Language is considered "perfected"... though not quite.

Complete core programming functional tools allow writting programs and libraries without imports.

(... within each of the 3 operator classes) makes reading code easier. Very simple parsing rules.