re = /<(mailto:[^\s@|]+@[^\s@|]+)\|([^\s@|]+@[^\s@|>]+)>/
str = 'this is test mail <mailto:demomail@gmail.com|demomail@gmail.com> testend'
subst = '<a href=\1>\2</a>'
puts str.gsub(re, subst)
cmUgPSAvPChtYWlsdG86W15cc0B8XStAW15cc0B8XSspXHwoW15cc0B8XStAW15cc0B8Pl0rKT4vCnN0ciA9ICd0aGlzIGlzIHRlc3QgbWFpbCA8bWFpbHRvOmRlbW9tYWlsQGdtYWlsLmNvbXxkZW1vbWFpbEBnbWFpbC5jb20+IHRlc3RlbmQnCnN1YnN0ID0gJzxhIGhyZWY9XDE+XDI8L2E+JwoKcHV0cyBzdHIuZ3N1YihyZSwgc3Vic3QpCg==