If I have a file that I want to monitor for any changes (other than looking at the file date stamps etc).
How could I perform a SHA1 hash on its contents?
I think this is what GIT does, so I just want to learn how to do it
- 3Is there a reason why you wouldn't just use a FileSystemWatcher? msdn.microsoft.com/en-us/library/…user1228– user12282009-12-28 15:29:35 +00:00Commented Dec 28, 2009 at 15:29
- 2Because it doesn't work, of course. Only on some supported file systems.Stephan Eggermont– Stephan Eggermont2009-12-28 15:42:26 +00:00Commented Dec 28, 2009 at 15:42
- @Will Even on supported file systems, it is not guaranteed to fire (limited buffer size).vossad01– vossad012017-03-13 15:20:28 +00:00Commented Mar 13, 2017 at 15:20
- @vossad01 unfortunate, but true.user1228– user12282017-03-13 15:25:02 +00:00Commented Mar 13, 2017 at 15:25
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2 Answers
using (FileStream stream = File.OpenRead(@"C:\File.ext")) { using (SHA1Managed sha = new SHA1Managed()) { byte[] checksum = sha.ComputeHash(stream); string sendCheckSum = BitConverter.ToString(checksum) .Replace("-", string.Empty); } } Calculate the checksum periodically.
2 Comments
Ta01
His question says "If I have a file that I want to monitor for any changes" , I read "File" , where do you see Directory?
For the specific application that you described, finding the SHA-1 hash of each file in the directory and then XORing them together would work well.
byte[] checksum = new byte[sha1Length]; for each file for (int index = 0; index < sha1Length; index++) checksum[index] ^= fileChecksum[index] Edited to Add: As pointed out in the comments, this won't really work. One specific scenerio would be adding two identical files, which would cancel each other out in the XOR. Perhaps creating a stream with all the file names and timestamps and file hashes and then hashing that would give you what you need.
Edited again: OK, now you've changed your question! So nevermind!
answered Dec 28, 2009 at 15:34
Jeffrey L Whitledge
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Kevin Montrose
xor isn't really advisable if security is a concern (he doesn't say it is, but maybe...). Instead I'd suggest sorting the files and hashing the hashes.