Create a sha256 catalog of a tar file passed on stdin.

tarripper

#!/bin/bash
# tarripper
# takes a tar file on stdin
# outputs a sha256 catalog of the tar file on stout
#
# public domain

set -e

while true; do
  IFS=''
  read -n 100 filename
  read -n 24 # mode, owner, group
  
  read -n 12 length_octal
  
  read -n 20 # last mod, checksum
  read -n 1 type
  read -n 188 # linked file, ustar, ustar version, owner name, group name, device major, device minor
  read -n 155 prefix
  if [ ! -z "$prefix" ] ; then prefix="${prefix}/"; fi
  read -n 12 # nothing

  
  length=$((0${length_octal}))
  blocks=$((length / 512))
  wholeblocks=$blocks
  remainder=$((length % 512))
  if [[ $remainder -gt 0 ]] ; then blocks=$((${blocks} + 1)); fi
  
  if [[ $type == "0" ]] ; then
    hash=$((dd ibs=512 count=$wholeblocks 2>/dev/null; dd ibs=$remainder count=1 2>/dev/null) | openssl dgst -sha256)
    dd ibs=1 skip=$(($blocks * 512 - $length)) count=0 of=/dev/null 2>/dev/null
    echo "$hash $prefix$filename"
  else
    # skip ahead
    dd ibs=512 skip=$blocks count=0 of=/dev/null 2>/dev/null
  fi
done