How do a binary diff on two identically sized files under linux?

Question

I have two identically sized files and I need to do a binary diff to check whether they're the same.

I'm currently runnnig diff file1.img file2.img but it's taking quite a while to process my 4GB files. Is this the most efficient way to do this?

Answer 1

cmp is designed to find differences in binary files. You might also try checksumming (sum) and compare the hashes.

Answer 2

One of the most common ways of determining if two files are identical (assuming their sizes match) is using a program to create a "hash" (essentially a fingerprint) of a file. The most common ones are md5sum and sha1sum.

For example:

$ md5sum file1 file2
e0e7485b678a538c2815132de7f9e878  file1
4a14aace18d472709ccae3910af55955  file2

If you have many files that you need to check, for example if you are transferring a directory full of files from one system to another, you can redirect the output from the original system to a file, then md5sum/sha1sum can automatically use that file to tell you which files are different:

$ md5sum file1 file2 > MD5SUMS
... copy file1, file2, MD5SUMS across
$ md5sum --check MD5SUMS
file1: OK
file2: OK

Answer 3

Found a solution - the cmp tool which comes with most Linux flavours.

Answer 4

If I just want to know if they are the same, I prefer to use sha1sum if it's available, or md5 as a fallback.

If I want to know how different they are, or where they're different, one thing that works is to crank them both through 'od' ('octal dump', which usually has a hex option) to make temp files and then diff those.