[fpc-pascal]Controlling TTY output

[Michael.VanCanneyt at Wisa.be]

On Tue, 31 Oct 2000, md wrote:

> FPC developers:
> 
> Here is a brain teaser.
> 
> Let us say we have two environments:
> 
> 1) Normal BASH shell with prompt in TTY1 -  The TERM environment
> variable will be set to linux
> 2) KDE Destktop - The TERM environment variable will be set to xterm
> 
> Under the non-x window environment, how do we fork() / execlp( ) another
> process so that the new child process
> will use a different Ttty console to output its writeln( ) information
> to.
> 
> Under KDE, I can execute a fork() with execlp( ) and the command line
> will be as follows 'konsole -e /bin/application arg1'
> 
> The net effect of this is that the parent process continues in its own
> console window and the child process will execute
> in a separte console window. The input/output of each process is now
> separate to each window.  
> 
> Under non-xwindows environments, .i.e. normal bash shell, How do we
> fork() / exec( ) a process so that it will be assigned a different TTY
> or some other means of having a separate console for each process.

under bash, one would type:

command args >/dev/ttyX 2>&1 </dev/ttyX &

or under csh

command args >& /dev/ttyX </dev/ttyX

(replace X with the terminal number)

The /dev/ files need the correct permissions, of course.

under FPC you would do the following;

  fork
  if pid=0 then
     // Child
    begin
    // Same effect as below may be gotten with dup2() !!
    Close(input);
    Close(output);
    Close(stderr);
    Assign(Input,'/dev/ttyx');
    Assign(output,'/dev/ttyx');
    Assign(stderr,'/dev/ttyz');
    Reset(input);
    Rewrite(output);
    Rewrite(stderr);
    Execlp('command','args')
    end
  else
    begin
    // Parent
   
    end;


> 
> What this also means that the login process for a given TTY is skipped
> or avoided so the processes that are started from
> the runlevel 3 inittab file can spawn processes that will take over a
> given console.

You'd better do that, yes.

> 
> This is different that just logging into a bunch of different consoles
> and running each process on a given console.  This is where the code is
> assigning processes to consoles.
> 
> Any help would be appreciated.

I hope the above helps.

Michael.