Gets information about the system.
Posix requires that you must not make any assumptions about the format of the values, e.g. you cannot rely on three digit version numbers or anything else returned by this function.
Returns a hash of strings with information about the system. The indices of the hash are
sysname - operating system name (e.g. Linux)
nodename - system name (e.g. valiant)
release - operating system release (e.g. 2.2.10)
version - operating system version (e.g. #4 Tue Jul 20 17:01:36 MEST 1999)
machine - system architecture (e.g. i586)
domainname - DNS domainname (e.g. example.com)
domainname is a GNU extension and not part of POSIX.1, so this field is only available on GNU systems or when using the GNU libc.