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Newsgroups: comp.lang.ada
Subject: Re: How to get the application path
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From: Markus E Leypold
 <development-2006-8ecbb5cc8aREMOVETHIS@ANDTHATm-e-leypold.de>
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Date: Tue, 24 Jul 2007 23:56:47 +0200
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> "Niklas Holsti" <niklas.holsti@nospam.please> wrote in message
> news:46a5e4e1$0$27850$39db0f71@news.song.fi...
> ...
>> If the Command_Name is simply "bong.exe", you cannot expect Full_Name to
>> search through the file system to find the directory that contains
>> "bong.exe". There could be several such directories. Full_Name cannot
>> use the PATH envinroment variable to find the directory because PATH
>> only applies to executable files and Full_Name should apply to all files.
>
> Well, on Janus/Ada the Path applies to all files (Open searches the path if
> given a simple file name). This cames from inadequate DOS documentation when
> we were building our compiler in the early 1980's, and an unwillingness to
> break existing code.
>
> Anyway, in Janus/Ada 95, all you do is open "Bong.Exe" and then ask for the
> Name; that will definitely find the file and return its full path. Not sure
> whether the Amendment updates will change that (probably not, it would break
> all of our code...).
>
>> If Command_Name gives you only the simple name, and you want the full
>> name, I think you must use Ada.Environment_Variables to get the value of
>> PATH and then scan the PATH directories for the Command_Name. But then
>> it would be simpler to just put the "application path" into a well-named
>> environment variable and forget about Command_Name.
>
> Yes, that's how you'd have to do it in general. Yuck. (At least you can do
> that with Ada.Directories.) I don't see how an Ada program could put the
> application path into an environment variable, though; this is the sort of
> thing that I wouldn't want to have to go outside of Ada to do (because it
> would depend on the user "doing the right thing", and we all know that users
> often don't do the right thing).

Now, on Unix I'd just put a shell script wrapper in place of the executable:

   MYPATH="$0"
   MYAPP="$(which $MYPATH.bin)"  # locate the executable proper

   export EXE_PATH="$MYPATH"

   exec $MYAPP "$@"

(untested, mind you).

That would even put the full path in argv[0]. The power of shell
script wrappers in Unix is usually underestimated.

Regards -- Markus





>
>                          Randy.