[SOLVED] Perl SHA256SUM Clarification

Sky.Crawler · 02-25-2011, 12:46 PM

I am writing a perl script to take the SHA256SUM of every image file in a directory. The problem is that the SHA256SUM created by perl is different than the one created by the straight sha256sum utility from the command line.

The perl script returns hashes much quicker than the command line, leading me to believe the image files are not actually being used, but some other value (like their names for instance).

I am using "strict" and "warnings", and no errors are being returned.

PHP Code:


			
use Digest::SHA;



# Code Omitted



opendir(my $dh, $STARTING_DIRECTORY) or die "Cannot open directory: $!";

while (readdir $dh)

{

    # Strip out the "." and the ".."

    unless ($_ eq '.' or $_ eq '..')

    {

        # Wrap up the filename for convenience

        # It's equal to the absolute path to the file

        my $absolute = "$STARTING_DIRECTORY$_";

        

        # Calculate SHA256SUM

        my $digest = Digest::SHA->new(256);

        $digest->add($absolute);

        my $hash = $digest->hexdigest();

        print $hash, " $_\n";

    }



# Code Omitted

Because these are image files, I do not need them to be read line-by-line, only in one piece, like the command line utility does it. How can I accomplish this?

bigearsbilly · 02-26-2011, 02:55 AM

if you want to slurp a whole file as one string:

Code:

local $/ = undef;

my $slurp = <>;

print "[$slurp]";

now your hash should work

http://perldoc.perl.org/perlvar.html

or better use Digest::File (I ain't tried it)

http://perldoc.perl.org/Digest/file.html

also, you can shortcut and use a glob pattern rather than readdir

@list = <*.img *.jpg>

it's easier to use find2perl to traverse directories.
perl programming is about laziness!

Sky.Crawler · 02-28-2011, 08:33 PM

It ended up being a simple fix.

All that had to be done was open the file and switch to a binary reading mode.

PHP Code:


			
open(FILE, "$STARTING_DIRECTORY$_") or die "ERROR. $_ could not be opened: $!";

        

# This is critical to prevent ulcers and create correct SHA256 checksums

binmode(FILE);



# Compute the SHA256 of the file

my $digest = Digest::SHA->new(256);

$digest->addfile(*FILE);

my $hash = $digest->hexdigest();