title: pipe dd to sha256sum
body: <p>I need to get the sha256 hash of a chunk of a binary file.
  I wrote a little shell script for that task:</p>
  
  <pre><code>dd if=$1 skip=$2 count=$3 bs=1 | sha256sum
  </code></pre>
  
  <p>When I test it, I get the following result:</p>
  
  <pre><code>bernardo@bernardo-ThinkCentre-Edge72:~$ ./test.sh test.bin 10 20
  20+0 records in
  20+0 records out
  20 bytes (20 B) copied, 0,000100981 s, 198 kB/s
  7d9330a7c51eabe36a81a6cff308ac4d2035e63d7a356fc112f4fcd16208f43d  -
  </code></pre>
  
  <p>Does that mean the hash is based solely on the chunk output by dd, or did it also use dd's feedback "20+0 records in..."?</p>