#!/usr/bin/perl -w

if ($#ARGV==-1 or $ARGV[0] =~ m!(--|-|/)h(elp)?!i) { print <<EOT ;
$0: count number of 1k fully-null blocks in a file

  This program takes a set of filenames on the command line.
Each one is scanned to find fully-null blocks that could be
the result of being a sparse file and might be left as holes
by some versions of tar (although I don't know the algorithm).
EOT
};

for (@ARGV) {
        $fn = $_;
	open F, "<$fn" or warn "Couldn't open '$fn'" and next;
        $blankblocks = 0;
        $size = (stat F)[7];
   if ($size == 0) {
        print "- $fn: zero-length file\n";
   } else {      
        bloop:
        while (0 != (read F,$_,1024)) {
            for (unpack 'I*',$_) {
                 if ($_ > 0) {
                      next bloop;
                 };
            };
            $blankblocks ++;

        };
        printf "- $fn: %d/%d blocks blank (%.1f%%)\n",
               $blankblocks,
               (($size-1)/1024)+1,
               ($blankblocks*1024.0/$size*100.0);
    };
};