PNGファイルを読み込み評価する

parse_png.sh

#!/bin/bash
set -eu
pngFile=$1
headPtr=0
if [ "89504E470D0A1A0A" != $(xxd -ps -u -s $headPtr -l 8 $pngFile) ]
then
  echo "pngファイルではありません"
  exit 1
fi
headPtr=$((headPtr+8))

chunkName=""
while [ "IEND" != "$chunkName" ] 
do
  chunkLength=$((0x$(xxd -ps -u -s $headPtr -l 4 $pngFile)))
  chunkName=$(dd if=$pngFile ibs=1 skip=$((headPtr+4)) count=4 2> /dev/null)
  checkSum=$(xxd -ps -u -s $((headPtr+4+4+chunkLength)) -l 4 $pngFile)
  printf "%04x: %s %04x\n" $headPtr $chunkName $chunkLength
  recount=$(printf "%08X" 0x$(dd if=$pngFile ibs=1 skip=$((headPtr+4)) count=$((4+chunkLength)) 2> /dev/null | cksum -o3 | cut -d " " -f 1 | xargs -I ZZ dc -e "16oAi ZZ p"))
  if [ "$recount" != "$checkSum" ]
  then
    echo "ファイルが壊れています"
    echo $recount is not equal to $checkSum
  fi
  headPtr=$((headPtr+4+4+chunkLength+4)) #to next chunk
done