[TUHS] Re: shells, Re: Listing of early Unix source code from the Computer History Museum.

Wikipedia content is a little better than LLM output, but not much! (The best thing in Wikipedia is the referencs.) The changes to the Thompson shell to make the PWB shell (which I guess Massey worked on; hence the name) are laid out pretty well in "UNIX Time-Sharing System: The Programmer's Workbench" (of which Massey is a co-author): https://archive.org/details/bstj57-6-2177 The projects which used PWB made extensive use of shell command files. So, PWB made two kinds of changes to the shell: i) flow-of-control commands used in shell procedures were made built-ins (which gave a huge decrease in fork() overhead), and ii) minor enhancements to shell command semantics (variables, evaluation of expressions, nestable control structure), which made shell command files much more powerful (and thus used a lot more). Minnie's 'version comparison tool' is useful to use to compare the 'Massey' shell: https://minnie.tuhs.org/cgi-bin/utree.pl?file=PWB1/sys/source/s2/sh.c with the vanilla V6 ('Thompson') shell. The PWB shell is definitely a tweaked version of the Thompson shell. Noel