Lexical Warnings

• Warnings now have scope (enclosing file, subroutine, or block).
• Enable with use warnings
• Squelch with no warnings

Example

    use strict;
    use warnings;

    my $a = undef;
    print $a, "\n";    # Waning emitted here

    {
      no warnings;     # Turn off warnings here
      print $a, "\n"   # No warning emitted
    }
  

Use of uninitialized value in print at lexwarn.pl line 5.