1_golfed.rb

a=n.gsub(?|,' ').split$/
i=!p;t=a.map(&:chars).transpose.map(&:join).select{i^=a}.sort_by{|s|s[/[A-Z]/][0]}
x=0;t.map{|t|y=0;u=p;t.chars{|c|u&&a[y][x,3]=?|*3;a[y][x+1]=c;y+=1;u|=c=='_'};x+=2}
a.join$/

sort_books.rb

def sort_books(n)
  a = n.gsub(?|,' ')  # pre-emptively remove all the '|'.
    .split $/         # and split into an array of lines
                      # ($/ is the INPUT_RECORD_SEPARATOR, typically "\n")
                      # we're going to write our answer into `a` later

  i = !p # i = true; we'll use this as a flip-flop variable
         # Kernel#p returns nil with no args

  # we're now going to get a sorted array of book titles (t)
  t = a.map(&:chars)  # break array into nested array of every character
       .transpose     # and transpose the entire array
       .map(&:join)   # this gives us an array of "horizontal" book titles with dividers

       .select { i ^= a } # select every second line
                          # (i.e. just titles without dividers)
                          # `i` starts off true
                          # `a` is truish (it's our original array)
                          # `^=` is the bitwise xor assignment,
                          #      it will alternate true/false on each execution

       .sort_by { |s| s[/[A-Z]/][0] } # sort by the first alphabetical char

  # use counters for less chars than `each_with_index`
  # x and y are cartesian coordinates in the final array

  x = 0 # start in the left-hand column

  # go through each title
  t.map { |t|
    y = 0 # each book title starts on the top row

    u = p # `u` is "have we reached the book's spine yet?" (or are we above it?)
          # `u` starts off false and we'll set it true when we see the first '_'
          # after which we'll start writing the book's edges

    # go through each character of each title, including leading spaces and '_'s
    # this will "descend" down the array writing each letter of the title
    # along with the "edges"
    t.chars { |c|

      u &&                  # if we're on the spine
        a[y][x,3] = ?|*3;   # write ||| in the next 3 columns
                            # the middle | will be overwriten by the title char

      a[y][x+1] = c; # write the current title char into the second (x+1) column

      y+=1; # descend to the next row

      u |= c == '_' # Since '_' is the top and bottom of the book,
                    # this toggles whether we're on the spine
    }
    x += 2 # jump to the right 2 columns and start on the next title
  }
  a.join $/ # hopefully this is obvious
end