Is there a command/program for OS X that allows me to hook to a file and display its changes in realtime without re-opening it, much like "top" monitors system processes in realtime?

3 Answers 3


You can use tail to monitor single log file.

If file is deleted, then created again you may want to use tail -F to actively monitor file changes

If same file is being appended too use tail -f to actively monitor file changes

  • 1
    It doesn't seem to display changes as the file updates
    – Mark
    Commented Feb 6, 2011 at 18:38
  • It does, at least on FreeBSD and linuxes. Should work on Mac OS X too.
    – gelraen
    Commented Feb 6, 2011 at 18:41
  • @Mark how do you modify the file during checking?
    – ulidtko
    Commented Feb 6, 2011 at 18:48
  • Perhaps it has something to do with the fact that the file is in a Dropbox and is updated perhaps a bit differently?
    – Mark
    Commented Feb 6, 2011 at 18:48
  • 2
    Try tail -F. Consult with man tail for more details about these options.
    – gelraen
    Commented Feb 6, 2011 at 18:51

Another alternative may be doing less the-interesting-file and hitting Shift+F.


If you are doing this on file sync'd by dropbox the chances are it is creating a new file with a different inode so the tail -f command and the less +F command do not work since they are still referencing the old file handle they opened initially.

I suggest trying

watch "tail /path/to/filename"

It feels hackish but at least every X seconds it will re run tail on the filename giving you the updated output regardless of whether or not the inodes change on the file.

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