File: autoconf.info,  Node: Systemology,  Next: Shellology,  Up: Portable Shell

11.1 Systemology
================

This section aims at presenting some systems and pointers to
documentation.  It may help you addressing particular problems reported
by users.

   POSIX-conforming systems (https://en.wikipedia.org/wiki/POSIX) are
derived from the Unix operating system
(https://en.wikipedia.org/wiki/Unix).

   The Rosetta Stone for Unix (https://bhami.com/rosetta.html) contains
a table correlating the features of various POSIX-conforming systems.
Unix History (https://www.levenez.com/unix/) is a simplified diagram of
how many Unix systems were derived from each other.

   The Heirloom Project (https://heirloom.sourceforge.net/) provides
some variants of traditional implementations of Unix utilities.

Darwin
     Darwin is a partially proprietary operating system maintained by
     Apple Computer and used by most of their products.  It is also
     known as macOS, iOS, etc. depending on the exact variant.  Older
     versions were called “Mac OS X.”

     By default the file system will be case insensitive, albeit case
     preserving.  This can cause nasty problems: for instance, the
     installation attempt for a package having an ‘INSTALL’ file can
     result in ‘make install’ reporting that nothing is to be done!

     Darwin does support case-sensitive file systems, but they must be
     formatted specially as such, and Apple discourages use of a
     case-sensitive volume for the base operating system.  To build
     software that expects case-sensitive filenames, it is best to
     create a separate disk volume or disk image formatted as case
     sensitive; this can be done using the ‘diskutil’ command or the
     Disk Utility application.

QNX
     QNX is a realtime operating system running on Intel architecture
     meant to be scalable from the small embedded systems to the hundred
     processor super-computer.  More information is available on the QNX
     home page (https://blackberry.qnx.com/en).

Unix version 7
     Officially this was called the “Seventh Edition” of “the UNIX
     time-sharing system” but we use the more-common name “Unix version
     7”.  Documentation is available in the Unix Seventh Edition Manual
     (https://s3.amazonaws.com/plan9-bell-labs/7thEdMan/index.html).
     Previous versions of Unix are called “Unix version 6”, etc., but
     they were not as widely used.