CTSS was developed during 1963 and 64. I was at MIT on the computer center staff at that time. After having written dozens of commands for CTSS, I reached the stage where I felt that commands should be usable as building blocks for writing more commands, just like subroutine libraries. Hence, I wrote "RUNCOM", a sort of shell driving the execution of command scripts, with argument substitution. The tool became instantly most popular, as it became possible to go home in the evening while leaving behind long runcoms executing overnight. It was quite neat for boring and repetitive tasks such as renaming, moving, updating, compiling, etc. whole directories of files for system and application maintenance and monitoring.
– Louis Pouzin, "The Origin of the Shell", https://multicians.org/shell.html