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).
You can use it to map the short name to the long name if you prefer, although people usually do it the other way around, to save on typing.
;)
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.
Fun stuff! Especially when combined with GNU parallel, in cases where the thing I'm measuring isn't already parallelized, and I want to be lazy.
Also does pv necessitate doing single threaded I/O?
> $ gzip -c access.log > access.log.gz
Is it?
tar -cz dir | base64
base64 -d | tar -xz
Works flawlessly to move configs and stuff between servers.
I actually love the blend between terminal and GUI. For this example I'm using CLI tools to produce text and I'm using GUI to scroll, select and copy&paste the text between two terminal tabs. I wish developers put more emphasis on empowering terminal with GUI capabilities.
tar cpS "$@" --sort=name | pv -bratpes $(du -cks "$@"|sed -n '/.total$/ s/.total$//p')k
,pv files/ | tar xp -C /destination
,pv files/ | ssh overthere tar xp -C /destination tar ... | dd status=progress | ...Sadly, dd will not give you an estimated time or allow you to limit the transfer rate, which are two features I use a lot in pv
Changing the endianness of the data?
That's just what I used it for, early in my career, in a software troubleshooting case.
I was a newbie dev, tasked with converting some data from another machine / OS format on tape to a Unix machine format.
Was fairly new to Unix too.
Looked through man pages, found dd, could read and copy the data from tape drive to disk using it. But the data, while in ASCII, and English letters, seemed garbled. Seemed like actual words, but not quite, if you know what I mean. Something seemed off a bit.
I puzzled over it for a while, then checked the dd man page again. I saw the conv=swab option and its meaning, which is to swap adjacent bytes. (Typical Unix cryptic syntax, and I say that as a long term Unix guy). I probably was new to endianess at that time. This was in a pre-Internet time, so I could not google to check what endianness meant.
I added that option to my dd command line, and what was my shock and pleasure to see all the words coming out as proper English words, now, on the screen!
Then I knew that the tape contained actual data, not garbage. I saved it to disk under some file name.
Job done.