Pipe viewer is excellent. I use it all the time.

As of version 1.8.10[1], which includes my merge request[2] to add an '--output' option, it has even completely replaced my use of 'dd' for writing disk images: 'sudo pv -Yo /dev/mmcblk0 whatever.img' is nicer, has much better progress indication, automatically selects a more sensible buffer size, and begets fewer groans from UNIX neckbeards, than the old 'sudo dd of=/dev/mmcblk0 if=whatever.img'. (The '-Y' causes pv to sync after each write, which greatly improves progress indication in Linux.)

Though it's useful for much more of course. I use it for progress when compressing files ('pv blah | gzip ...'), when uploading files to the web ('pv blah | curl --upload-file - ...' — curl doesn't show progress when uploading for whatever reason), or just when I wanna see that something is happening with an operation which would otherwise take a while (even things like a slow 'du -h /some/path | sort -h' benefits from a 'pv' squeezed in the middle just to indicate that something is happening).

[1] https://codeberg.org/a-j-wood/pv/releases/tag/v1.8.10

[2] https://codeberg.org/a-j-wood/pv/pulls/90

> This example shows that the access.log file is being read at the speed of 37.4MB/s but gzip is writing data at only 1.74MB/s. We can immediately calculate the compression rate. It's 37.4/1.74 = 21x!

No you cannot:

1. Compression algorithms buffer a lot and will have have tendencies to perform large burst writes and in particular large writes on final flush. Instantaneous measurements will therefore not be particularly useful.

2. Compression ratio refers to the average across an entire file, as entropy is not uniform across the input unless you are compressing just noise or just zeros. Some sections might compress extremely well while others do not and end up consuming more space than the input due to overhead.

pv is great.

It has a limit parameter so you can limit the speed. Great if you don't want to saturate some link or have additional costs for uploading above a certain rate per hour/day.

Also useful for testing behaviour on slow filesystem / connections.

It can take a pid argument too, -d IIRC, which will get it to display progress info for all the open file descriptors of a running process.

Really useful as a quick way to check what a IO process is doing if appears to be stuck.

There's also `progress` which works for tools mainly operating on a single file, but unlike `pv`, you don't have to start the tool differently. It'd e.g. work nicely for the `gzip` example. Just call `progress` on a different terminal while `gzip` is running.

Pipe viewer? What's that? Let me check the post...oh, it's good old pv! Never noticed it had a full name, damn Unix utilities with their short names!