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

for me easiest to use and best looking so far is command pv or bar like some guy already wrote

for example: need to make a backup of entire drive with dd

normally you use dd if="$input_drive_path" of="$output_file_path"

with pv you can make it like this :

dd if="$input_drive_path" | pv | dd of="$output_file_path"

and the progress goes directly to STDOUT as this:

    7.46GB 0:33:40 [3.78MB/s] [  <=>                                            ]

after it is done summary comes up

    15654912+0 records in
    15654912+0 records out
    8015314944 bytes (8.0 GB) copied, 2020.49 s, 4.0 MB/s