new feature: run program on first connection / run program on last

disconnection

I was looking to trigger an action when I connect to shairport.
Basically, I want to switch on the stereo when I start playing music
over shairport (and I want to switch if off when I stop streaming).

Because my set-up will be different than any other set-up, I thought
about making it generic.

Two new command-line options --play_prog and --stop_prog take one
argument: the command line to start when the first connection is made or
when the last connection quits.

Example:
$ shairport.pl --play_prog="amixer set PCM 100%"

shairport.pl

@@ -71,6 +71,9 @@
 my $mac;
 # SB volume
 my $volume;
+# custom play and stop program
+my $play_prog;
+my $stop_prog;
 # output debugging information
 my $verbose;
 # where to write PID
@@ -97,6 +100,8 @@
           "s|squeezebox" => \$squeeze,
           "c|cliport=s" => \$cliport,
           "m|mac=s" => \$mac,
+          "play_prog=s" => \$play_prog,
+          "stop_prog=s" => \$stop_prog,
           "l|volume=s" => \$volume,
           "h|help" => \$help);
 
@@ -117,6 +122,8 @@ sub usage {
           "  -c  --cliport=port              Sets the SBS CLI port\n",
           "  -m  --mac=address               Sets the SB target device\n",
           "  -l  --volume=level              Sets the SB volume level (in %)\n",
+          "      --play_prog=cmdline         Program to start on 1st connection\n",
+          "      --stop_prog=cmdline         Program to start on last disconnection\n",
           "  -d                              Daemon mode\n",
           "  -w  --writepid=path             Write PID to this location\n",
           "  -v  --verbose                   Print debugging messages\n",
@@ -491,6 +498,11 @@ sub performSqueezeboxSetup {
             if (defined($squeeze) && $squeeze) {
                 &performSqueezeboxSetup();
             }
+
+            # the 2nd connection is a player connection
+            if (defined($play_prog) && $sel->count() == 2) {
+                system($play_prog);
+            }
         } else {
             if (eof($fh)) {
                 print "Closed: $fh\n" if $verbose;
@@ -502,6 +514,11 @@ sub performSqueezeboxSetup {
                     eval { kill $conns{$fh}{decoder_pid} };
                 }
                 delete $conns{$fh};
+
+                # 1 connection means no connection
+                if (defined($stop_prog) && $sel->count() == 1) {
+                    system($stop_prog);
+                }
                 next;
             }
             if (exists $conns{$fh}) {