On 2021-06-28 20:01:03 +0700, Robert Elz via austin-group-l at The Open Group wrote: > if a utility is invoked with any of stdin/out/err closed then what happens > is very explicitly unspecified in POSIX. My guess is that that is largely > because if the utility then opens a file it will be given a fd that > corresponds to the (or one of the) closed stdin/out/err streams, and truly > bizarre things are likely to happen - but that kind of issue is not stated > as the reason, you simply get unspecified behaviour if a utility is > started that way.
POSIX defines the EBADF error as Bad file descriptor. A file descriptor argument is out of range, refers to no open file, or a read (write) request is made to a file that is only open for writing (reading). So, if writing to a closed fd yields unspecified behaviour, what does "refers to no open file" mean? > austin-group-l@opengroup.org (really Geoff Clare) said: > | The error occurred, and because of it the utility did not do what it is > | supposed to do. > > That's debatable. The outcome was not what was desired, but the utility > did exactly what was required of it, it determined (one assumes for this > purpose, where this fails truly is an error to be reported) the current > working directory and printed it, then exited, with no errors reported to > it. > > You might prefer that it "fflush(stdout); if (ferror(stdout)) ..." but > there's nothing explicit in the standard that says that it has to do that. But the standard says "shall write", and knowing that this may or may not succeed, it is the responsibility of the shell to check that it has succeeded. Otherwise, there would be no way to check data integrity with a shell script. Note that ISO C has similar wording for fclose(): "The fclose function returns zero if the stream was successfully closed, or EOF if any errors were detected." But AFAIK, everyone assumes that it is the responsibility of the implementation to detect any error. -- Vincent Lefèvre <vinc...@vinc17.net> - Web: <https://www.vinc17.net/> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/> Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
