I often find it handy to watch how a variable is changed by tieing it and monitoring what tie methods are called. Here's an easy way to do it.

use strict;
use warnings;
{
   package Debug::Tie::StdScalar;
   use Tie::Scalar;
   use Carp;
   sub AUTOLOAD {
      our $AUTOLOAD =~ s/Debug:://;
      carp join " >|< ", "calling $AUTOLOAD", @_[1..$#_], "";
      goto &$AUTOLOAD;
   }
}

# example use
my $x;
tie $x, 'Debug::Tie::StdScalar', 4;
print $x;
$x = 3;
$x .= "abc";
++$x;
[download]

If tracking multiple tied variables, try something like this instead:

use strict;
use warnings;
{
   package Debug::Tie::StdScalar;
   use Tie::Scalar;
   use Carp;
   sub TIESCALAR {
      my $obj = &Tie::StdScalar::TIESCALAR(@_);
      carp join(" >|< ", "calling Tie::StdScalar::TIESCALAR", @_[1..$#
+_]),
           "\n=> ", 0+$obj;
      $obj;
   }
   sub AUTOLOAD {
      our $AUTOLOAD =~ s/Debug:://;
      carp join " >|< ", "calling $AUTOLOAD", 0+$_[0], @_[1..$#_], "";
      goto &$AUTOLOAD;
   }
}
[download]

Replace Scalar and SCALAR with hash or array to watch aggregates.

Update: An obvious enhancement is to catch and show what FETCH returns; up to now I haven't needed to do so, so it is left as an exercise for the reader.

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