different checksum of original file and copied file

Question

I am running a script that copy a file from one location to other. In script I am calculating MD5sum using below command of original file and copied file and they are different:

echo -n "file" | md5sum

How come a same file have different MD5sum? Does copy command change something in Linux? I have also checked checksum using cksum filename and it is also coming different.

Solution

echo -n "file" | md5sum

You are not calculating the checksum of the file, but of the filename. It is probably different because you are using two different paths (echo -n "/old/path/to/file" | md5sum vs. echo -n "/new/path/to/file" | md5sum).

To calculate the md5sum of the file, use this command:

md5sum file

Comments

[Infotechie]

Thanks Martin.I have one more confusion that if a file is zipped into tgz then untar it. Then the both original and untar file will also have the same checksum or different?

[Martin von Wittich]

If you compare the original file with the zipped tgz file - no, they will not have the same checksum. If you extract the tgz file and compare the extracted file with the original file - yes, they must have the same checksum.