How to add a progress bar to a shell script?

When scripting in bash or any other shell in *NIX, while running a command that will take more than a few seconds, a progress bar is needed. For example, copying a big file, opening a big tar file. What ways do you recommend to add progress bars to shell scripts?

[takc923]

前からずっと疑問だったけど"\n"じゃなくて"\r"するだけでいいのか。なるほど。