Why does shasum generate non-standard hashes? As far as I can tell, the shasum that ships with os x doesn't generate the hashes that it's supposed to.

$ echo "" | /usr/bin/shasum
adc83b19e793491b1c6ea0fd8b46cd9f32e592fc ?-


When I look up empty string sha hash in wikipedia I see that I should expect to get

da39a3ee 5e6b4b0d 3255bfef 95601890 afd80709


My reading of the man page for shasum is that it defaults to sha 1. I get the same result even if I specify sha 1. 

What's going on here?

ps Apologies for the bad tag. I can't create a tag of sha or shasum due to low reputation...
shasum is working fine but echo "" doesn't produce an empty string:

pse@Fourecks:~$ echo "" | od
0000000    000012                                                         
0000001


This works better:

pse@Fourecks:~$ echo -n "" | shasum
da39a3ee5e6b4b0d3255bfef95601890afd80709