Sites/materiais bons:

• http://bash.cyberciti.biz/guide/Main_Page - Muito bom
• http://aurelio.net/shell/ - Muito bom também
• http://www.thegeekstuff.com/2010/06/bash-array-tutorial/
• http://www.thegeekstuff.com/2010/11/50-linux-commands/
• https://github.com/jlevy/the-art-of-command-line
• http://redsymbol.net/articles/unofficial-bash-strict-mode/
• https://github.com/alebcay/awesome-shell
• https://github.com/koalaman/shellcheck