Very Computer

Hello,
     I am new to this list, and I am not completely sure that this
message doesn't belong on comp.lang.c.

     I am trying to write a C program to operate a display on an xterm,
and as such I would like to read the environment variables COLUMNS and
LINES to know what size window I am dealing with.  I am running Debian
Linux on my home PC, and hence I use the bash shell.  The problem with
bash is that the COLUMNS and LINES environment variables are not
exported to the shell environment.   Hence a call to getenv() does not
find them.  I realize that perhaps using system("export COLUMNS") and
then searching the environment might work, but this seems like a hack,
and I am not sure I want my program to go around modifying its parent's
environment.  Is there anyway to get at these local environment
variables without exporting them?

Thanks in advance,
Larry Gariepy

 Larry> Hello,
 Larry>      I am new to this list, and I am not completely sure that
 Larry> this message doesn't belong on comp.lang.c.

I think you made the right choice.

 Larry>      I am trying to write a C program to operate a display on
 Larry> an xterm, and as such I would like to read the environment
 Larry> variables COLUMNS and LINES to know what size window I am
 Larry> dealing with.  I am running Debian Linux on my home PC, and
 Larry> hence I use the bash shell.  The problem with bash is that the
 Larry> COLUMNS and LINES environment variables are not exported to
 Larry> the shell environment.  Hence a call to getenv() does not find
 Larry> them.

 Larry>  I realize that perhaps using system("export COLUMNS") and
 Larry> then searching the environment might work

It doesn't.

 Larry> but this seems like a hack, and I am not sure I want my
 Larry> program to go around modifying its parent's environment.

You can't do that anyway.

 Larry> Is there anyway to get at these local environment variables
 Larry> without exporting them?

No.

You have two main approaches. One is to export LINES and COLUMNS in
the shell first (they should always be exported, really).

The other approach is to get the window size from the tty device
using TIOCGWINSZ.

--
Andrew.

comp.unix.programmer FAQ: see <URL: http://www.erlenstar.demon.co.uk/unix/>
                           or <URL: http://www.whitefang.com/unix/>

Quote:>exported to the shell environment.   Hence a call to getenv() does not
>find them.  I realize that perhaps using system("export COLUMNS") and

  export COLUMNS LINES

in your .profile or .bashrc.  Poof, they'll always be in the environment.
Alternately, you could find the code to the resize command, which queries
the terminal screen size.

-- Lars

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