Assignments and Expressions

  [Literals]      sh-array      array=(a b c)   array[1]=B   "${a[@]}"
                  sh-assoc      assoc=(['a']=1 ['b']=2)   assoc['x']=b
  [Operators]     sh-assign     str='xyz'
                  sh-append     str+='abc'
  [Builtins]      local   readonly   export   unset   shift
                  declare   typeset   X let
