I want to grok how fast a particular file is growing.

I could do

watch ls -l file

And deduce this information from the rate of change.

Is there something similar that would directly output the rate of growth of the file over time?

5 Answers 5


tail -f file | pv > /dev/null

But beware that it involves acually reading the file, so it might consume a bit more resources than something that watches just file size.

  • This does a nice job - just to save someone else a search or two - you'll need to yum install pv on a Centos/Redhat system to be able to do this ;-) Commented Jan 2, 2018 at 16:19
  • or brew install pv on macOS
    – oligofren
    Commented Nov 20, 2023 at 3:32

progress (Coreutils progress viewer) or recent versions of pv can watch a file descriptor of a particular process. So you can do:

lsof your-file

to see what process ($pid) is writing to it and on which file descriptor ($fd), and do:

pv -d "$pid:$fd"


progress -mp "$pid"
  • Here's a convenient bash function that uses this nice solution, just pass it the file name: `function watchgrow() { lsof $1 | grep $1 | head -n 1 | sed -r 's/ +/ /g' | cut '-d ' -f2,4 | sed -r 's/ +/:/g' | xargs pv -d } ~
    – Omer
    Commented Jan 31, 2020 at 23:10
  • @Omer That's vastly complicated for something it has built-in :-) Just pass the filename directly: pv -s @tmp.tgz tmp.tgz > /dev/null will give you the ETA.
    – oligofren
    Commented Nov 20, 2023 at 3:40
  • @Stephane: I installed coreutils using Homebrew and there was no progress command built-in per 2023.
    – oligofren
    Commented Nov 20, 2023 at 3:42

I have a little perl script that I put in my bash environment as a function:

fileSizeChange <file> [seconds]

Sleep seconds defaults to 1.

fileSizeChange() {
  perl -e '
  $file = shift; die "no file [$file]" unless -f $file; 
  $sleep = shift; $sleep = 1 unless $sleep =~ /^[0-9]+$/;
  $format = "%0.2f %0.2f\n";
    $size = ((stat($file))[7]);
    $change = $size - $lastsize;
    printf $format, $size/1024/1024, $change/1024/1024/$sleep;
    sleep $sleep;
    $lastsize = $size;
  }' "$1" "$2"

The following shell function monitors a file or directory and shows an estimate of throughput / write speed. Execute with monitorio <target_file_or_directory>. If your system doesn't have du, which could be the case if you are monitoring io throughput on an embedded system, then you can use ls instead (see comment in code)

monitorio () {
# show write speed for file or directory
    size=$(du -ks "$target" | awk '{print $1}')
    echo ""
    while [ 1 ]; do
        size=$(du -ks "$target" | awk '{print $1}')
        #size=$(ls -l "$1"  | awk '{print $5/1024}')
        kb=$((${size} - ${prevsize}))
        kbmin=$((${kb}* (60/${interval}) ))
        # exit if this is not first loop & file size has not changed
        if [ $firstrun -ne 1 ] && [ $kb -eq 0 ]; then break; fi
        echo -e "\e[1A $target changed ${kb}KB ${kbmin}KB/min ${kbhour}KB/hour size: ${size}KB"
        sleep $interval

example use:

user@host:~$ dd if=/dev/zero of=/tmp/zero bs=1 count=50000000 &
user@host:~$ monitorio /tmp/zero
/tmp/zero changed 4KB 24KB/min 1440KB/hour size: 4164KB
/tmp/zero changed 9168KB 55008KB/min 3300480KB/hour size: 13332KB
/tmp/zero changed 9276KB 55656KB/min 3339360KB/hour size: 22608KB
/tmp/zero changed 8856KB 53136KB/min 3188160KB/hour size: 31464KB
user@host:~$ killall dd; rm /tmp/zero
  • 1
    Thanks this worked great! I made a few small modifications if anyone is interested. My file transfer was spotty so I turned off stopping the script when the file size doesn't change, also added an optional second parameter to set the interval, and no longer printing the text on the first run since it's always 0: gist.github.com/einsteinx2/14a0e865295cf66aa9a9bf1a8e46ee49
    – Ben Baron
    Commented Aug 24, 2018 at 16:55
  • 1
    Thanks! I had to use the commented out ls version on Mac.
    – Ehren
    Commented Sep 8, 2021 at 17:14
  • I also had to do set -k to get it to ignore the # lines on Mac/zsh. Commented Aug 2, 2022 at 8:02
tail -f -c 1 file | pv > /dev/null

A variation on the other answer, the -c 1 means start from the last byte of the file, which avoids having to read in the last ten lines first (which can take a while on binary files).

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