in reply to X or console?

I made a quickie module (sorry, can't post it) for work. A first-check is for the environment variable DISPLAY. If you don't have it, the user's not accessing the shell with an X service available. This is pseudocode: 
sub hasX
{
   return undef if not defined $ENV{DISPLAY};
   return undef if port_not_listening($ENV{DISPLAY});
   return 1;
}

[download]
It's not foolproof. But after you get a hint from these, you can look at CPAN's X11 modules for more support.

--
[ e d @ h a l l e y . c c ]

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Re: Re: X or console?
by bobn (Chaplain) on Jul 23, 2003 at 18:53 UTC

    What is your port_not_listening()? here's mine: 

    sub port_not_listening
{
# UNTESTED
my $timeout = 10;
my ($remote, $port) = split(/:/, $_[0]);
    
    $iaddr   = inet_aton($remote) or return 1;
    $paddr   = sockaddr_in($port, $iaddr);

    $proto   = getprotobyname('tcp');  # X uses tcp, right?
    socket(SOCK, PF_INET, SOCK_STREAM, $proto)  or die "socket: $!";

    eval
    {
        local $SIG{ALRM} = sub { die "connection timeout\n" }; 
        alarm $timeout;
        connect(SOCK, $paddr) or die "$! for $remote\n";
        alarm 0;
    };

    return 1 if ( $@ );
    return 0;
}

    [download]

    Update: Halley points out correctly (below) that the line my ($remote, $port) = split(/:/, $_[0]); is unlikely to actually yield a correct port number.

    --Bob Niederman, http://bob-n.com
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[d/l]
[select]
      Generally, $ENV{DISPLAY} isn't going to give an exact port number. The typical X11 setup assumes (TCP 6000 + $port) where $port is what you find in the variable. There are more complicated port configurations like "localhost:1.1", though, so I didn't go into lengthy discussion. Use the X11 modules which presumably do it right.

      --
      [ e d @ h a l l e y . c c ]

[reply]
[d/l]

        Theat's the part that's untested. Damn, I remembered the colon, but forgot that wat's after it is frequently some number that would be silly at best as a port number. (I think I confused it with the way X connections tunneld in ssh look in netstat output, which is on the order of localhost:6012). DRAT!

        Given a correct IP and port, the rest of the code should be good because it's extracted from code I actually use. But the ($addr, $port) = split(/:/, $ENV{DISPLAY}) is almost certain not to yiled a good port.

        --Bob Niederman, http://bob-n.com
[reply]

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