Tweaking Bash 'cd' and TAB completion to recognize spelling mistakes

Completion is a feature of readline.

You can enable case insensitive completion either by:

1) Adding to your ~/.bashrc:

bind 'set completion-ignore-case on'

2) Adding to your /etc/inputrc:

set completion-ignore-case on

Notes:

/etc/inputrc, as @mak comments, effects all shells that use readline, and not just bash.
This will make all completions case insensitive.

CodeHunter