Bash

Bash is the default shell for Gentoo linux, and the language upon which its package manager specification is built.

Resources

 * Chet's Bash page
 * Official Bash documentation
 * Short Bash reference from the Gentoo dev manual.
 * The Bash FAQ and Bash guide on Greg Wooledge's wiki.
 * bash-hackers wiki (very good reference)
 * Bash gitweb
 * POSIX sh spec
 * mksh, ksh93, and ksh88 manuals for cross-reference.

Remember, almost all shell programming resources, including books, are garbage. Don't trust anything found on Google.