How to add a progress bar to a shell script?

Question

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 b

Answer 1

I was looking for something more sexy than the selected answer, so did my own script.

Preview

Source

I put it on github progress-bar.sh

progress-bar() {
  local duration=${1}


    already_done() { for ((done=0; done<$elapsed; done++)); do printf "▇"; done }
    remaining() { for ((remain=$elapsed; remain<$duration; remain++)); do printf " "; done }
    percentage() { printf "| %s%%" $(( (($elapsed)*100)/($duration)*100/100 )); }
    clean_line() { printf "\r"; }

  for (( elapsed=1; elapsed<=$duration; elapsed++ )); do
      already_done; remaining; percentage
      sleep 1
      clean_line
  done
  clean_line
}

Usage

 progress-bar 100