better validation, better formatting

dragonbat

@@ -49,17 +49,24 @@ sub perc {
 
 sub charge_time {
     my ($data) = @_;
-    return $data->{full} ? "--:--" : stime($data->{tcharge});
+    return "--:--" if $data->{full} || $data->{tcharge} == 0;
+    return stime($data->{tcharge});
 }
 
 sub drain_time { 
     my ($data) = @_;
+    return "--:--" if $data->{tdrain} == 0;
     return stime($data->{tdrain});
 }
 
 sub main {
     if (@ARGV) {
         my $t = $ARGV[0];
+        # require a positive number of seconds (e.g. 2, 4.5, 0.2, ...)
+        unless ($t =~ m/^([1-9][0-9]*(\.[0-9]+)?|0\.[0-9]*[1-9][0-9]*)$/) {
+            print "usage: $0 [POLL-SECS]\n";
+            exit(1);
+        }
         do {
             run();
             select(undef, undef, undef, $t);