my @uptimes = qw(1 2 3 4 5 1 2 3 4 1 2 3 4 5 6);

for (0 .. $#uptimes) {
  print "We have a peak value: $uptimes[$_]\n"
    if  $_           == $#uptimes
    or  $_           <  $#uptimes 
    and $uptimes[$_] >  $uptimes[$_+1];
}