Oct
30
Written by:
cadams
10/30/2007 9:03 AM
So sometimes we nee to answer that age old problem of comparing two files. We need to make sure that they are the same or that they are different. This is an old topic and often times can be beaten to death. It's often times used as an educational example that many folks implement themselves when learning a new language. Here is a quick little script I wrote many moons ago that compares two hashes.
It takes two operands. The two operands it takes are the fully-qualified path names to the files. It has minimal error checking, so please be careful about where you use it or if you need a more robust solution for your specific problem.
$md5 = new-object System.Security.Cryptography.MD5CryptoServiceProvider;
$file = get-item -path $args[0];
$file2 = get-item -path $args[1];
if ( $file.Exists -eq $False ) {
write-host "File doesn't exist!";
}
else {
[byte[]] $original = [System.IO.File]::ReadAllBytes(($file.DirectoryName + "\" + $file.Name));
[byte[]] $newer = [System.IO.File]::ReadAllBytes(($file2.DirectoryName + "\" + $file2.Name));
$oldresult = $md5.ComputeHash($original);
$newresult = $md5.ComputeHash($newer);
$i = 0;
while ($i -lt $oldresult.Count) {
if ($oldresult[$i] -eq $newresult[$i]) {
$i++;
}
else {
$false;
break;
}
}
}
There you have it. Please note that it does not return a result when the hash is the same. It will only return and return a value of false. Take note that I am taking a shortcut inside the else clause of the while loop. I'm cheating here a bit that if the value is not the same between the pair of indexed bytes our entire sum is borked. We no longer need to go through comparing to the end of our two hashes. They don't match and that's all we need to know. Which is why I call break to stop the while loop, we then fall out of the execution with nothing else to do.
It doesn't have any higher intelligence such as commenting on which pair of files didn't match, etc. But it can be reworked to have that intelligence. I actually had a script which called this script and I encapsulated the higher intelligence into the invoking script. If the script got a false result it knew the two didn't match and would take appropriate action.
In my next blog post I'll be posting up one of my Cmdlets. It'll be written in C# and I'll be contributing it to the ScriptVault. That'll be my first foray into noodling with the Vault. It'll be my way of giving something back to the community. I'd like to have it be something really useful that people will get some value from. I'd like to in my own part give a little something back to our growing little garden of a community. I know that I have my own plans to get a business license and to sell some of the Cmdlets I've written in a similar fashion like those fine folks at '/n Software' and their own Cmdlets. However I'd like to contribute one of the ones that I am most proud of among my collection.
I think I know which one I'll be contributing too. It's one that I have considered submitting to the Pscx team and if they want I can refactor it or provide a submission to their codebase for the next release. never having dabbled in such things I'll have to see if there are any coding standards or if there is a quality bar that needs to be met prior to submission, etc, etc.
2 comment(s) so far...
Re: MD5Sum Two Files.
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By hexi on
9/26/2011 7:57 PM
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Re: MD5Sum Two Files.
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