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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Beginner in Mac OS X, and ADA and gtkAda:    $prefix,
 and what bin, and home is usr/bob or OSX Users/bob
Date: Tue, 12 Sep 2017 08:33:09 +0100
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Date: 2017-09-12T08:33:09+01:00
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Mace Ayres <mace.ayres@gmail.com> writes:

> New to Mac OSX. Various software instructions may say home directory;
> is that OS X ./USERS/Me
> or Unix's /usr/me:

It's wherever you get to when you log in! (also, the value of the HOME
environment variable). Mine, on macOS, is /Users/simon

> Sometime they refer to the bin directory. Which bin?
>
> Some instructions say $prefix .. what prefix is that?

When a Unix-style application is installed, all its components will be
under some directory.

System utilities will be under /usr normally, and the layout is fairly
standard: /usr/bin, /usr/include, /usr/lib etc.

Non-system utilities should be somewhere else, not least so that the
base system is still usable and can still be upgraded.

A typical place would be under /usr/local. But if you use just this, you
can end up with different utilities clashing; and you can't easily
remove a utility that you no longer need (I realise that package
managers such as RPM, aptitude, macports & homebrew achieve this too).

As far as I can remember, GNAT GPL wants to install under
/usr/local/gnat; I don't like this, because I want to keep different
versions on my machine. On Windows, GNAT caters to this by installing
under C:\GNAT\2017 for example.

So, I install GNAT GPL under /opt/gnat-gpl-2017 etc and FSF GCC under
/opt/gcc-7.1.0 etc. (the /opt comes from, I think, Solaris).

The layout of the compiler under that directory is the same, so it's
handy to have a way of referring to that directory. $prefix is that way!

That name is used because most Unix build tools (I mean, the tools for
building the application) use an environment variable $prefix for this
purpose.

But, it's only a handy name for "wherever you installed the application"
- there's no actual variable involved.