How does progress(1) work?

We’ll cover a neat little utility called progress(1). Many common utilities like cp or gzip don’t spit out a progress bar by default. progress finds those processes and estimates how far along they are with their operation. For example, if you’re copying a 10Gb with cp, running progress will indicate that it’s progressed 1Gb, and has another 9Gb to go.

Here’s an example, kindly borrowed from the project’s README: