Scsh is a Unix shell in that is has significant syntax extensions to make writing Unix shell scripts easy (constructing pipelines, setting I/O redirection, conditional execution etc.). It also offers access to lower-level functionality like all Posix system calls, TCP/IP sockets and a full-featured regular expression library. This is embedded into a general-purpose programming language with real data types, extensive, syntactically clean control constructs and "real" quoting rules. Scsh is also a full implementation of R4RS Scheme with some non-standard behavior (required for scripting). As a result, a wide variety of existing Scheme code can be used. The underlying Scheme implementation is a virtual machine for compact byte code.