If `pv` doesn't know the input size, it doesn't show it. In your case, it can determine that its stdin is a file by looking at the `/proc/self/fd/0` symlink:

If `pv` doesn't know the input size, it doesn't show it. In your case, it can determine that its stdin is a file by looking at the `/proc/self/fd/0` symlink: $ ls -l /proc/self/fd/0 < /tmp/x lr-x------ 1 user users 64 <date> /proc/self/fd/0 -> /tmp/x