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Comment by j3097736 | Hacker News Reader

>pv < image.iso > /dev/sdb

Huh? pv can cat stuff on it's own, and it will be able to make a progress bar based on the filesize

  pv image.img > /dev/sdb

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Okay. I don't actually use pv, so I was just extrapolating from the original post. In any case, cat is definitely the wrong choice.

So I suppose that the command

    pv < image.iso > /dev/sdb

would actually need to buffer the complete file, before commencing to write to the device (and showing the progress), which would defeat the whole idea of showing progress.

It wouldn't. It just won't be able to predict a file size.

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

From what I can tell, bash uses 4K buffers for pipelines.

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