creating a file downloading script with checksum verification

Question

I want to create a shellscript that reads files from a .diz file, where information about various source files are stored, that are needed to compile a certain piece of software (imagemagick in this case). i am using Mac OSX Leopard 10.5 for this examples.

Basically i want to have an easy way to maintain these .diz files that hold the information for up-to-date source packages. i would just need to update these .diz files with urls, version information and file checksums.

Example line:

libpng:1.2.42:libpng-1.2.42.tar.bz2?use_mirror=biznetnetworks:http://downloads.sourceforge.net/project/libpng/00-libpng-stable/1.2.42/libpng-1.2.42.tar.bz2?use_mirror=biznetnetworks:9a5cbe9798927fdf528f3186a8840ebe

script part:

while IFS=: read app version file url md5
do 
  echo "Downloading $app Version: $version"
  curl -L -v -O $url 2>> logfile.txt
  $calculated_md5=`/sbin/md5 $file | /usr/bin/cut -f 2 -d "="`
  echo $calculated_md5    
done < "files.diz"

Actually I have more than just one question concerning this.

1. how to calculate and compare the checksums the best? i wanted to store md5 checksums in the .diz file and compare it with string comparison with "cut"ting out the string
2. is there a way to tell curl another filename to save to? (in my case the filename gets ugly libpng-1.2.42.tar.bz2?use_mirror=biznetnetworks)
3. i seem to have issues with the backticks that should direct the output of the piped md5 and cut into the variable $calculated_md5. is the syntax wrong?

Thanks!

Answer 1

while IFS=: read app version file url md5
do
  echo "Downloading $app Version: $version"
  #use -o for output file. define $outputfile yourself
  curl -L -v  $url -o $outputfile 2>> logfile.txt
  # use $(..) instead of backticks.
  calculated_md5=$(/sbin/md5 "$file" | /usr/bin/cut -f 2 -d "=")
  # compare md5
  case "$calculated_md5" in
    "$md5" )
      echo "md5 ok"
      echo "do something else here";;
  esac
done < "files.diz"

Answer 2

The following is a practical one-liner:

curl -s -L <url> | tee <destination-file> |
sha256sum -c <(echo "a748a107dd0c6146e7f8a40f9d0fde29e19b3e8234d2de7e522a1fea15048e70  -") ||
rm -f <destination-file>

wrapping it up in a function taking 3 arguments: - the url - the destination - the sha256

download() {
   curl -s -L $1 | tee $2 | sha256sum -c <(echo "$3  -") || rm -f $2
}

Answer 3

My curl has a -o (--output) option to specify an output file. There's also a problem with your assignment to $calculated_md5. It shouldn't have the dollar sign at the front when you assign to it. I don't have /sbin/md5 here so I can't comment on that. What I do have is md5sum. If you have it too, you might consider it as an alternative. In particular, it has a --check option that works from a file listing of md5sums that might be handy for your situation. HTH.