SVN: and bash: How to tell if there are uncommitted changes

I'm trying to wrap a standard sequence of steps in a shell script (linux/bash) and can't seem to figure out how to tell if the execution of svn status returned anything. For example

~/sandbox/$svn status
?       pat/foo
~/sandbox/$echo $?
0

If I delete the foo file, then the

svn status

return nothing, but the echo $? is still 0

I want to not do some steps if there are uncommitted changes.

Pointers greatly appreciated.