class NameError

def missing_name

# => "HelloWorld"
end
e.missing_name
rescue NameError => e
HelloWorld
begin

Extract the name of the missing constant from the exception message. 
def missing_name
  if /undefined local variable or method/ !~ message
    $1 if /((::)?([A-Z]\w*)(::[A-Z]\w*)*)$/ =~ message
  end
end

def missing_name?(name)

# => true
end
e.missing_name?("HelloWorld")
rescue NameError => e
HelloWorld
begin

Was this exception raised because the given name was missing? 
def missing_name?(name)
  if name.is_a? Symbol
    self.name == name
  else
    missing_name == name.to_s
  end
end