On Tue, 10 Aug 2021 23:39:47 +0700 Robert Elz wrote: > Date: Tue, 10 Aug 2021 10:22:29 -0400 > From: Chet Ramey <chet.ra...@case.edu> > Message-ID: <731876fc-39c0-4388-0c9e-bf560921b...@case.edu> > > | In this case, you are using features outside what POSIX specifies. > > Using a variable name that's outside what POSIX specifies is hardly > using a feature that's outside POSIX - if it were then there would be > no safe non-trivial scripts, since any variable name might be made magic > by some shell or other (and no, there's nothing special about all upper > case variable names). Only those defined by POSIX to have some special > meaning mean something, and even those can be re-used for another purpose > as long as one doesn't expect the special behaviour to function correctly.
Quoting POSIX.1-2017 on environment variables [1]: Environment variable names used by the utilities in the Shell and Utilities volume of POSIX.1-2017 consist solely of uppercase letters, digits, and the <underscore> ( '_' ) from the characters defined in Portable Character Set and do not begin with a digit. Other characters may be permitted by an implementation; applications shall tolerate the presence of such names. Uppercase and lowercase letters shall retain their unique identities and shall not be folded together. The name space of environment variable names containing lowercase letters is reserved for applications. Applications can define any environment variables with names from this name space without modifying the behavior of the standard utilities. So, no matter if "special" or not by your standards, there is definitely a significant difference between "all upper case" variable names and the rest, which IMO in itself constitutes a sufficient argument for sticking to non-all-caps variable names for custom functionality (AKA "applications" above or one's own shell scripts). [1] https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html -- Štěpán
