?perl -e"$line = undef; print 3 + $line"
3
?perl -e"$line = undef; print '3' . $line"
3
?perl -e"$line = undef; print 3 unless $line"
3
?perl -e"$line = undef; print 3 unless defined $line"
3

##</code><code>##

$current_time='14:30:05'
(undef, $min, $sec)=split /\:/, $current_time