(Just first question here ...) Early BSD shells could look at first bytes (0404) to indicate was a pascal object to run the Berkeley pascal interpreter. When csh was introduced, the csh would run the other shell /bin/sh if the first character was not a # pound. So csh used the single # as magic to run the script with csh. The # was a comment for csh, make, and awk (but not for standard sh which could use a : colon for the comment). Have a look at top of 4BSD's /usr/src/sys/newsys/sys1.c below. This code is not in v7 nor 32V. The system has been changed so that if a file being executed begins with the magic characters #! , the rest of the line is understood to be the name of an interpreter for the executed file. Previously (and in fact still) the shell did much of this job; it automatically executed itself on a text file with executable mode when the text file's name was typed as a command. Putting the facility into the system gives the following benefits. 1) It makes shell scripts more like real executable files, because they can be the subject of 'exec.' 2) If you do a 'ps' while such a command is running, its real name appears instead of 'sh'. Likewise, accounting is done on the basis of the real name. 3) Shell scripts can be set-user-ID. 4) It is simpler to have alternate shells available; e.g. if you like the Berkeley csh there is no question about which shell is to interpret a file. 5) It will allow other interpreters to fit in more smoothly. To take advantage of this wonderful opportunity, put #! /bin/sh at the left margin of the first line of your shell scripts. Blanks after ! are OK. Use a complete pathname (no search is done). At the moment the whole line is restricted to 16 characters but this limit will be raised.

reason I asked was my memory was #! in 1978 or so. But that's now sounding like I compressed time a bit. On Mon, Dec 28, 2020 at 6:08 PM Clem Cole <clemc(a)ccc.com> wrote: