Some years ago I read a book about shell scripting; AFAIR it was called something like "Teach yourself shell scripting in 24 hours" by Sams publishing. The author of the book had the (nice) idea of creating a library with shell functions that can be used over and over by system administrators, shell programmers, and generally users who enjoy typing on a terminal.

I decided to take the library and extend it. Thus, whenever I find a useful function I add it, and whenever I encounter a bug I am trying to fix it. I named the library shell-utils because this is what it really is. To use shell-utils simply add it to your shell's environment. For example, this is how my .bashrc entry looks like:

if [ -f ~/bin/shell-utils.sh ]; then
   . ~/bin/shell-utils.sh
fi

Even though the library contains around fifteen functions, I found out that the most useful (at least if you are working with many different file types) are file_to_lower, file_to_upper and ren_all_suff, ren_all_pref.