$;      The subscript separator for multi-dimensional  array
             emulation.   If  you  refer  to an associative array
             element as
                  $foo{$a,$b,$c}

             it really means

                  $foo{join($;, $a, $b, $c)}

             But don't put

                  @foo{$a,$b,$c}      # a slice--note the @

             which means

                  ($foo{$a},$foo{$b},$foo{$c})

             Default is "\034", the same as SUBSEP in awk.   Note
             that  if  your  keys contain binary data there might
             not be any safe value for $;.  (Mnemonic: comma (the
             syntactic  subscript separator) is a semi-semicolon.
             Yeah, I know, it's pretty lame, but  $,  is  already
             taken for something more important.)