Command for reloading file from disk to show changes when using “less?”

In less is there a command for reloading a file from disk, so that less will show any changes made to a file since less was started? This would saving me have to terminate and restart less if I want to see changes to the file I'm viewing.

Dan Stevens

Posted 2017-07-21T15:17:42.257

Reputation: 220

So you mean instead of following data appended to a file using something like tail -f -n 200 some_file.txt you would want less to reload the file but only show changed content that could be anywhere in the file? Beginning middle or end? – JakeGould – 2017-07-21T15:23:16.400

Answers

There are two possibly relevant commands detailed in the fine manual for less(1)

   R      Repaint the screen, discarding any buffered  input.   Useful  if
          the file is changing while it is being viewed.

   F      Scroll  forward, and keep trying to read when the end of file is
          reached.  Normally this command would be used  when  already  at
          the  end of the file.  It is a way to monitor the tail of a file
          which is growing while it is being  viewed.   (The  behavior  is
          similar to the "tail -f" command.)

thrig

Posted 2017-07-21T15:17:42.257

Reputation: 686

R for repaint does not always reload the file.^[1]

A workaround that always reloads the file is to press hq, which will open the Help page, then quit. It has a side effect of forcing the file to reload.

[1] Here are some examples of situations that R do and do not reload:

> and >> changes: DO get reloaded
sed -i, gEdit, TextEdit: DO NOT get reloaded
On Linux, vi changes: DO get reloaded
On Mac, vi changes: DO NOT get reloaded

I believe the difference comes down to whether the inode changes (you can check with ls -i foo.txt). If the inode changes, then R will not work.

wisbucky

Posted 2017-07-21T15:17:42.257

Reputation: 1 522

works for me on Mac. less --version gives less 487 (POSIX regular expressions) – john sullivan – 2019-04-17T15:30:02.397

1@johnsullivan Thanks for the comment. I revisited my answer and found that it depends on the situation. When using vi to edit on Mac, R doesn't work. But vi on Linux does. See my revised answer for more details. – wisbucky – 2019-04-17T19:11:37.557