I get different results from the Linux command "sha256sum" and the Pony stdlib "Digest" functions.

Using the command line:
  echo "123456" | sha256sum
  e150a1ec81e8e93e1eae2c3a77e66ec6dbd6a3b460f89c1d08aecf422ee401a0  -

Using the Pony program shown below:
  sha256 of '123456' is 8d969eef6ecad3c29a3a629280e686cf0c3f5d5a86aff3ca12020c923adc6c92


use "crypto"

actor Main
  new create( env: Env ) =>
    let input = "123456"
    let hasher = Digest.sha256()
    try hasher.append( input ) end
    let binhash = hasher.final()
    // Convert the binary hash to a hex string.  We know the length
    // will be twice as long so we can preallocate enough space.
    let hexhash = String( binhash.size()*2 )
    var i: USize = 0
    while i < binhash.size() do
      let byte = try binhash(i) else 0 end
      hexhash.push( _hexdigit((byte and 0xF0 ) >> 4))
      hexhash.push( _hexdigit( byte and 0x0F ))
      i = i + 1
    end
    env.out.print("sha256 of '"+input+"' is "+hexhash)

  fun ref _hexdigit( n: U8 ): U8 =>
    try "0123456789abcdef"(n.usize()) else '0' end