On Sat, Jan 21, 2023, 8:45 AM Clem Cole wrote: > Certainly fd 2 as a error output appears with Lesk's portable C library, > which was included in V6 - see the last para on page 1 of his document: > > "Initially you are given three file descriptors by the system: 0, 1, and > 2. File 0 is the standard input; it is normally the teletype in > time-sharing or input data cards in batch. File 1 is the standard output; > it is nor- mally the teletype in time-sharing or the line printer in batch. > File 2 is the error file; it is an output file, nor- mally the same as file > 1, except that when file 1 is diverted via a command line ’>’ operator, > file 2 remains attached to the original destination, usually the terminal. > It is used for error message output. These popular UNIX conventions are > considered part of the C library specification. By closing 0 or 1, the > default input or output may be re-directed; this can also be done on the > command line by >file for output or > This document pre-dates ditroff. The idea/names of stdin/out/err (as > opposed to fd 0, 1, 2) does not come about until Dennis does "typesetter C" > which is described in K&R. > > That said, my memory is fd 2 as ana error path was there in Fourth or > Fifth Edition, before Lesk did this library -- i.e. it was a convention > that Dennis/Ken et al were all using -- when it is realized that printing > errors on in the same output flow as the standard (normal) output was > problematic in a pipe stream. > ᐧ > It looks to be a mixed bag in 5th edition. Cc, ac, comm and find all printf the errors. Diff uses writes to fd 2. I didn't catalog further, but this kinda looks like a developing convention, not yet fully realized. . Warner On Fri, Jan 20, 2023 at 5:46 PM ron minnich wrote: > >> I am trying to remember when fd 2 (aka stderr) became a thing. I have a >> vague memory that it was post-v6 but that may be way off. >> >> >>