I have an ant target that runs some scripts on some Amazon EC2 instances. So, I first generate a file with a list the hostnames of the running instances. Then, ant runs a shell command that iterates over the hostnames and runs ssh to each with a command. Since I didn't want to run the command as root, the command was su -c "\"command with some parameters\"" username, which worked fine for me. However, on cygwin on Microsoft Windows, the nested quoting didn't work, so that su was trying to set the user to the first command parameter rather than the username I specified. None of the variations of single and double quotes and backslash quoting the space characters worked.

Finally, I gave up on trying to deal with the quirks of the Bourne shell under Microsoft Windows, and moved the su into a script on EC2:

if [ ! `id -un` = username ]; then su -c "sh -c \"$0 $*\"" username; exit; fi

Of course, none of the command parameters are expected to have spaces in them, as the $* would be trouble. And $@ wouldn't help because of the nested quoting.