Using MD5 checksum utility on Mac OS X

If you might be aware, every Linux distribution comes with the MD5 checksum utility - md5sum. Similarly UNIX flavors like Mac OS X, come pre-bundled with utility called md5

The OS X md5 utility can be found at /sbin/md5

I'll quickly show some steps on how to use it :

• Open Terminal

• Create a blank empty file anywhere on the system (I mean just anywhere) using touch

Eg : touch test.xml

• Now type the following to generate the md5 checksum of this file 

Eg : md5 test.xml > test.xml.md5

That's it. Now open the test.xml.md5 using TextEdit or Text Wrangler and you'll see the file's equivalent md5 checksum. 

If you want to change the format of the output similar to Linux's md5sum use the -r switch 

Eg : md5 -r test.xml > test.xml.md5

Note that MD5 checksums are used to verify the integrity of a file. Even a single new character added to the file will change the equivalent md5 output. Check for yourself. Modify the test.xml by adding some content to it. Now run the md5 utility again as shown above. The md5 equivalent of the file will now be different. The checksums are important to verify that the files / resources are intact throughout and ensure that they are not corrupt or tampered.

You can use this method to verify the integrity of zip or tar files that you download from the internet.

A free utility Checksum Validator is also available. At the heart of it's gui, it uses this md5 command.

This information can come particularly handy while using Maven as well. Suppose for some odd reason, you have to manually create md5 checksums of the dependency jar's - then this method tells you how to do it.