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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.ada
Subject: Re: ACCESS TO SYSTEM VARIABLES
Date: Mon, 07 Mar 2011 14:51:03 -0800
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Date: 2011-03-07T14:51:03-08:00
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Emile8 <pocchiola.yves@gmail.com> writes:
> On Linux I want to know the number of lines and columns of my working
> terminal. When on the command line I call by hand the system variables
> $LINES and $COLUMNS, I get the right answers.
>
> When I try to do the same from a program written in Gnat Ada 2005
> (Year 2010) using the specialized package Ada.Environment_Variables,
> as in the following code called from the same terminal, I get no
> answer for COLUMNS and LINES as if the corresponding system variables
> do not exist (I get a correct answer for PATH).
>
>
> with Ada.Environment_Variables; use Ada.Environment_Variables;
> with Ada.Text_Io; use Ada.Text_Io;
>
> procedure Print_Env is
> begin
> Put_Line("Columns : " & Value("COLUMNS"));
> Put_Line("Lines : " & Value("LINES"));
> Put_Line("Path : " & Value("PATH"));
> end Print_Env;
>
>
> I would like to understand the reasons of this behavior. Are there
> different kinds of system variables in Linux ? Those as HOME, PATH
> whose values depend only on the user session and those as LINES,
> COLUMNS defined for each used terminal. Is there a way in Ada to
> overcome this limitation ?

$LINES and $COLUMNS are bash shell variables, not environment
variables.  They're not visible from your Ada program any more than
variables declared within your Ada program would be visible from
a shell (even if the shell was launched by your Ada program).

bash probably obtains the values by invoking the ioctl() system
call with TIOCGWINSZ as the second argument.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"