[tylerchr]

pv is invaluable but my issue with it is it’s only useful if you think to include it before you run the command. Usually the thought doesn’t occur to me until I have some runaway cp or dd and I want to be reassured that it’s going to be done soon. For that case that this looks super interesting.

[rlpb]

You can attach pv to an existing process. IIRC it's the -p option.

[everybodyknows]

-p is same as "--progess":

https://linux.die.net/man/1/pv