Why is my command-line hash different from online MD5 hash results?

On a Mac OS X v10.5 (Leopard) PowerPC, if I do:

echo "hello" | md5 

b1946ac92492d2347c6235b4d2611184

But if I enter hello into one of the online MD5 hash sites like http://md5online.net/, I get:

5d41402abc4b2a76b9719d911017c592

Am I doing something wrong? If I want to use MD5 on the go, how can I make sure what I'm getting on the command line will agree with the online md5 tools?

When you echo from the command line, md5 is calculating the sum of 6 characters - h,e,l,l,o plus newline. The text you enter in a website doesn't have a newline.

Try doing

echo -n hello | md5

and it'll give you what you expect. The -n tells echo not to output a newline.

You can also use printf instead of echo, which automatically suppresses the newline character:

printf hello | md5

Or even:

printf "hello" | md5