I'd use `od`

    od -cvAnone -w1

This lists characters, showing `\escapes` for non-displayables.

So, to list the uniques:

    od -cvAnone -w1 | sort -bu

Or to produce a top-20 histogram:

    od -cvAnone -w1 | sort -b | uniq -c | sort -rn | head -26

See it **[Live On IdeOne]()**

     54     
     19    o
     17    e
     16    s
     14   \n
     14    n
     13    -
     12    t
     10    r
     10    i
      9    d
      8    c
      8    a
      6    u
      6    h
      5    |
      4    w
      4    v
      4    p
      4    l
      4    *
      4    `
      3    O
      3    b
      3    A
      3    1