Bash shell scripting

• Bash shell scripting - 10 second guide
• Tips For Robust Bash Scripts
• BASH Programming - Introduction HOW-TO
• Advanced Bash-Scripting Guide
• Conditions in bash scripting (if statements)
• Better Bash Scripting in 15 Minutes
• The Bash-Hackers Wiki
• bash -- Standard Shell

Other:

• Collection of Less Commonly Used UNIX Commands
• Ten things I wish I knew earlier about the Linux command line
• commandlinefu.com - Command-line gems