@array = ('a');
foreach (@array) {
   # $_ is an alias for $array[0].
   local $_ = $_;  # This $_ is not an alias for $array[0].
   while (<DATA>) { }
   # $_ is clobbered, but not $array[0]
   print("[$_]$/");      # Prints "[]"
}
print("[$array[0]]$/");  # Prints "[a]"