"readlink" gets the original path of a symlink; what's the equivalent for Mac aliases?
After more googling, I was able to pull together the pieces for an osascript command:

alias_path="your/alias/path"
osascript -e 'tell application "Finder"' -e "posix path of (original item of alias file (posix file \"$alias_path\") as text)" -e 'end tell'