ascsh is a wrapper for the new ActionScript Compiler 2.0. It was modeled to be roughly equivalent to the older Flex Compiler’s fcsh and fcshd. It improve AS3/AIR/SWF/SWC project compilation performance by maintaining a persistent JVM compiler process.
The tool is followed by a daemon named ascshd, which is a convenience wrapper around ascsh itself. It starts a background server thread to maintain the ascsh process, and sends commands to it for builds. This way, the build can simply call ascshd again and again from the build system (no fussy shell) and it just gets faster over time.