You can shoot out one of the files in a .zip with something like this: 
open my $ZIP, '+<', 'test.zip';
local $/ = undef;
my $data = <$ZIP>;
my @offset;
while ($data =~ /PK\x03\x04/g) { # find all file headers
   push @offset, pos($data) - 4;
}
print "Found headers at: @offset\n";
substr($data, $offset[1]+14, 1) ^= "\x01"; # change the crc
seek $ZIP, 0, 0;
print $ZIP $data;

[download]
(This isn't foolproof, but probably good enough.) The structure of a zip file is described here: Zip (file format)#File headers

In reply to Re^3: File integrity checker by no_slogan
in thread File integrity checker by roperl

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