What is the difference between idn and idn2?

what is the difference between idn and idn2 ? (why two that do almost the same. why the output is different. Which one should be used) infile: Amazon.com ama--zon.com a--mazon.com --amazon.com amazon--.com amazon-.com cat infile | idn Amazon.com ama--zon.com a--mazon.com --amazon.com amazon--.com amazon-.com cat infile | idn2 amazon.com ama--zon.com a--mazon.com idn2: toAscii: string start/ends with forbidden hyphen (for 3 last entry) THK **Update:** This is the answer what i'm looking for. Thanks. Vote close. GNU IDN Library - Libidn Please be aware that GNU libidn2 is the successor of GNU libidn. It comes with IDNA 2008 and TR46 implementation and also provides a compatibility layer for GNU libidn.