Here's a summary of ways to protect yourself from accidentally deleting files:
Make rm -i less painful (article 23.6).
Write a "delete" script that moves "deleted" files to a temporary directory (article 23.8).
has an rmstar variable that makes the shell ask for confirmation
when you type something like
Use a more comprehensive "safe delete" program, like the one described in article 23.9.
Use revision control (article 20.12).
Make your own backups, as explained in article 20.2.
Prevent deletion (or renaming or creating) of files by making the directory (not necessarily the files in it!) unwritable. Article 22.2.
If you want to delete with wild abandon, use rm -f (article 23.10).