Nix: Monitor the progress of data through a pipe

You can use pv to monitor the progress of any pipe, by putting it between input/output pipes.

Example:

$ dd if=/dev/urandom | pv | dd of=/dev/null
1,74MB 0:00:09 [ 198kB/s] [ <=> ]

You could specify the approximate size with the --size if you want a time estimation.

You can also use it to output to stdout:

$ pv /home/user/bigfile.iso | md5sum
50,2MB 0:00:06 [8,66MB/s] [==>  ] 49% ETA 0:00:06

Note that in this case, pv recognises the size automatically.

Using pv can prove extremely useful when working with big files or processes taking a long time to complete. For example you can keep track how fast a file is transferred with nc command:

pv myFile | nc -w 1 example.com 3000

Via enkipro.com.