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I like the watch command, but it has its limitations.

I'm curious to know whether I could mimic the functionality of watch with less. I'm mainly looking for the ability to scroll through my directory as it dynamically gets modified via a running script.

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up vote 56 down vote accepted

In less, you can type F to keep reading at the end of a file (like tail -f); you can type :e and a file name to view a different file, but unfortunately, if you enter the name of the current file, less doesn't reload the file. However there's a trick to make it re-read the current file, suggested by sabgenton: type :e and enter the name of a non-existent file; that causes less to display an error message and then reload the current file.

If you're looking for an alternative to watch ls, here are a few:

  • Modern file managers (e.g. Nautilus, Thunar, Konqueror, Dolphin, Finder) refresh views in real time.
  • Emacs doesn't have real-time refresh, but with auto-revert-mode, it will reload the file or directory every 5 seconds (the delay is configurable).
  • Although w3m is primarily a web browser, it makes a passable directory and text file viewer. Press R to reload the (local) URL.
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For me :e randomnamejkdlfjldf fails to load the non-existent filename then reloads back to the current file :D – sabgenton Mar 18 at 10:36
@sabgenton Thanks, I didn't know that. That's a great trick. I added it to my answer, but you could post it as an answer of your own (which I hope Zaid would accept). – Gilles Mar 18 at 16:14
What if the file contents change but changes aren't necessarily appended. As in the file contents may be replaced completely, or partially. Does less +F deal with such a thing? – CMCDragonkai Apr 19 at 9:01
@CMCDragonkai No, less +F only watches for appended content. Use :e nonexistentfile to re-read completely changed input. – Gilles Apr 19 at 11:08
Is there a command line flag for that? – CMCDragonkai Apr 19 at 11:18

Shift+F will make less similar to tailf. That is, it gets refreshed if more data is appended to the file.

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Simply type:

less +F filename

This emulates pressing "F" within the editor.

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The "F" key when running less will do a "follow" similar to tail -f, but I'm not sure if that will achieve what you're looking for here.

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You can use vim to read the file then add the following mapping to your .vimrc file and you can easily reload a file with ,r:

let mapleader = ","
nnoremap <leader>r :edit <CR>

Note if you edited the file already, vim will complain. Just change to

let mapleader = ","
nnoremap <leader>r :edit! <CR>

To ignore changes.

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I normally use shift+G,shift+G to tail the output, or file, on a one-time basis. I find it especially helpful over a a network file system like CIFS.

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You could pipe it to tail -f instead, it would result in you following the output. You'd be losing the ability to move (scroll) through your output though.

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