Use (car (process-lines ...)) instead of (shell-command ...)
shell-command assumes Bourne-shell-compatible quoting, which doesn't work when the user isn't using a Bourne-compatible shell. Instead of futzing about with quoting, we can just use process-lines to execute a process and pass it arguments directly.
Scenario: I use rc as my main shell, which doesn't treat double-quotes specially or use backslashes for escaping characters. It isn't possible for me to run geiser without this patch.