It's a really minor point, but this statement is not strictly true:

  print "'$_' is empty string" if $_ =~ /^$/;
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What you want is /^\z/, since /^$/ will also match a single newline, as evidenced by the following test:

print "Empty   matches ^\$  --> ", ("" =~ /^$/ ? 'yes' : 'no'), "\n";
print "Newline matches ^\$  --> ", ("\n" =~ /^$/ ? 'yes' : 'no'), "\n"
+;
print "Empty   matches ^\\z --> ", ("" =~ /^\z/ ? 'yes' : 'no'), "\n";
print "Newline matches ^\\z --> ", ("\n" =~ /^\z/ ? 'yes' : 'no'), "\n
+";
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