Is it part of any standard (e.g. POSIX), that system files should be lower case

filenamesfilesystemsposix

My company resells an application whose brand name is mixed case, for example "ApplicationName".

The application's installer creates all paths and file names in this standard. E.g. The main directory is /opt/ApplicationName, the init file is called ApplicationName so I have to run service ApplicationName status and so on.

To me, this breaks all sensible conventions and I feel the files and directories should all be lower case (there is precedent in other applications such as MySQL, whose files and dirs are all called mysql, even applications like Apache and Tomcat do away with the preceding upper case letter).

If I raise this as a bug report, I'd like to put up a stronger argument than just "I think it's wrong". So is it dictated in something like the POSIX standard that system files like this should be lower case?

Best Answer

The POSIX standard has a section with guidelines for conforming utilities (i.e., "such as those written specific to a local system or that are components of a larger application") that says

Utility names should be between two and nine characters, inclusive.
Utility names should include lowercase letters (the lower character classification) and digits only from the portable character set.

[ref: 12.2 Utility Syntax Guidelines]

It's unclear to me whether the use of the words "should include" really means "should only include". (The consensus in the comments below is that it means "should only include").

An application on a Unix system that does not claim to be a POSIX conformant utility may otherwise use whatever name it wants. If it does claim to be a POSIX conformant utility that is part of the POSIX shell utilities, the text after the guidelines in section 12.2 says that "should" changes meaning to "shall".

There are no similar guideline regarding directory names as far as I know. macOS (which is a certified UNIX 03 product when running on an Intel-based Mac computer) uses /Users as the prefix for user's home directories, for example, as well as a number of other mixed-case directory names.

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Does POSIX guarantee that the standard utilities are in PATH

Yes and no. In a POSIX environment, the utilities must behave as described by the specification. In practice, this means that conforming versions of the utilities must be present in $PATH. However, when running your program on a POSIX-compliant system, you may be running it in a non-conforming environment. In practice, what often happens is that the OS has a legacy mode and a POSIX mode, and is in the legacy mode by default. Worse than missing some commands, the legacy mode tends to have incompatibilities in them, such as options with different meanings.

You can retrieve a good PATH with getconf. Of course, it's tricky, as getconf in the original $PATH may not be the right one. The Application Usage for command shows a way to do it:

command -p getconf PATH

As far as I understand the specification, this is not necessary if you are running your program in a POSIX-conforming environment; and if you aren't running your program in a POSIX-conforming environment, POSIX doesn't apply. However, this application usage can be taken as a recommendation: if this doesn't work, you can feel entitled to complain to your vendor that whatever they are doing regarding the letter of the POSIX spec, they are not complying with its spirit.

Should a serious student of *nix choose a distribution that is POSIX-compliant to learn standard features well

If I were in your boat, I'd pick something fairly user friendly and probably similar to the OS's you've used in the past. With Linux the top two contenders for desktop users are Fedora and Ubuntu. Fedora is the community edition (essentially) of Red Hat Enterprise Linux which is the most popular distribution used in the enterprise/government. A lot of people say they like Ubuntu though, I haven't used it to much to come to an opinion either way. Just pick something desktop-oriented like that, so that you can live your normal life and just go down to the command line or use some tool when you have a particular self-imposed homework assignment you want to finish.

POSIX is something for software developers and enterprise systems administrators to worry about, not someone just starting out. Most POSIX drafts standardize things like the options command line tools offer and API definitions. Occasionally, a POSIX standard will set some operational requirements for a system, but even then, that's too fine a point to worry about at your level of knowledge. The skills you're learning will be largely transferable outside of Linux (not completely, though). Even with POSIX, by design it only defines a certain subset of OS functionality, there are things (like diagnostic utilities, volume management, log formats and locations, package management, firewall implementations, etc) that exist outside of any POSIX standard that you'll have to interact with on the regular. Even the stuff that is standardized will often have language like "Whether X and Y will be left to implementation." And that's supposing the given vendor hasn't made the conscious choice to deviate from POSIX (as GNU/Linux does from time to time).

No matter what other people may say or how much stock they put in POSIX, all POSIX does is keep certain key features of the OS consistent across vendors. There will always be a substantial learning curve when moving to a different OS. You actually want it that way though. If things didn't change, then vendor solutions would be limited to the exact features that the working group was able to support (given how slow IEEE moves sometimes, that list of features would be small and slow to be filled out). You want vendor choice because having multiple ways of solving the same problem is a good thing.

Best Answer

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