Bash Language Grammar.
- http://man7.org/linux/man-pages/man1/bash.1.html
- http://www.opensource.apple.com/source/bash/bash-23/bash/parse.y
- https://github.com/atom/language-shellscript/blob/master/grammars/shell-unix-bash.cson
- http://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html
- http://stackoverflow.com/questions/10586153/bash-split-string-into-array