>perl -wMstrict -le
"for my $String (@ARGV) {
   my ($Site_Code, @RS) =
     grep defined,
     $String =~ m{ \A (...) .{4} | \G (\d) }xmsg
     ;
   local $\" = q{' '};
   print qq{site code: '$Site_Code'  digits: '@RS'};
   }
"
uk1sxve01205.gfjgjf5.fdhd5  usasxve513.gfdhf4.hgfd4
site code: 'uk1'  digits: '0' '1' '2' '0' '5'
site code: 'usa'  digits: '5' '1' '3'