Programmable Command Language
Programmable Command Language (PCL) was created at Carnegie Mellon University to enable the development of new commands to be invoked from the command line of DEC TOPS-20 mainframes, which were in heavy use in universities from the late 1970s through the 1980s. It is not connected with the printer command language PCL.
TOPS-20 had a very advanced command line interface with some user-friendly features such as context-sensitive help and suggested command completion while a command was being input from a terminal. PCL allowed developers to interface with this system to provide similar help and completion functions for the commands they were developing.
A set of structured programming constructs, described in the reference guide as "ALGOL-like", was provided, along with commands geared toward specific TOPS-20 features including access to its filesystem.
PCL programs were created as plain-text files, then compiled into TOPS-20 executables.