Re: How to find directory where the program is?

[nickroberts@ukf.net (Nick Roberts)]

On Wed, 24 Apr 2002 11:38:02 -0400, Hyman Rosen <hyrosen@mail.com> strongly
typed:

>Preben Randhol wrote:
>> How can one in Ada95 find out from which directory the Ada program is
>> stored in.  I mean I need to find out if my program is stored in
>> /usr/bin/ or /usr/local/bin or some other directory.
>
>There is no a priori reason for this to even be possible. Your Ada
>program could be loaded in PROM on your toaster, and even in UNIX,
>the same executable file could have many links to it in different
>directories, with different names.

Furthermore, one has to ask the question "why?" (Why do you wish your
program to discover its own executable?) As Hyman points out, there may not
be one (there may zero or several), but even if there is one, your program
may not have (any) access permission to it. (Side Issue 1, see below.)
Actually, what kind of access would you require?

Side Issue 1. It may just be me, but I would suggest that (on a well
managed system ;-) the vast majority of Ada programs will not need to, and
should not, have any access to their own executables. (If you're wondering
why, think about how viruses propagate themselves.)

If your program is, say, a discombobulator, and supposing it needs to add
itself to a cron-list (or equivalent), in order to complete one of its
actions perhaps, I would suggest you: (a) try to find a program argument
named say "-phase2" and use the value of the argument following it; (b) if
that fails, get the value of the environment variable named say
"discombob2"; (c) if that fails, use whatever strategy you do to obtain the
program's configuration file, and search for a line there beginning with
"phase2=" and use the remainder of the line; (d) if that fails, obtain the
configuration file's directory D and use D & Ada.Command_Line.Command_Name;
(e) if that fails, use D & Default_Program_File_Name (which you have
defined, e.g. a function which returns "discombob" under UNIX systems and
"DISCOMB.EXE" under DOS/Windows). (Simple ;-) Your program installer should
generate a configuration file with e.g.
"phase1=C:\SUPASOFT\BOBULTNS\DISCOMB.EXE" and
"phase2=C:\SUPASOFT\BOBULTNS\DISCOMB.EXE" in it, so that your program is
spared the effort (and hit-and-miss qualities) of trying to find out the
incantation necessary to run itself, and so that users are given maximum
flexibility in managing their system.

Hope this post has some element of enlightening qualities. (Not really sure
if it does; that's how posts go sometimes :-)

-- 
Nick Roberts