I'm looking for a CLI tool which will watch a directory and spit out the names of files that change in real time.

some_watch_command /path/to/some/folder | xargs some_callback

I'm aware of inotify (inotify-tools?) and it seems to be what I need, but I need something that is both Linux (in my case Ubuntu) and OSX compatible.

It doesn't need to be lightning fast, but it does need to trigger upon changes (within a second is reasonable). Also, I don't necessarily need the exact CLI program mentioned above. If some underlying tech exists and is easily scriptable on both platforms that would be great too.


OS X would typically use Folder Actions or Launchd for this task.

The only cross-platform tool I know is the watchdog API for Python (thus available for OS X and Linux). Install it through pip (or easy_install)

pip install watchdog

It comes with the watchmedo command line tool, which allows you to run shell commands on system events. Check its general syntax with watchmedo --help

Here is a short example, where you could easily modify the command and the path highlighted in bold:

watchmedo shell-command \
    --recursive \
    --command='echo "${watch_src_path}"' \

This would simply spit out the paths to all changed files or folders, allowing you to pipe watchmedo's output to another shell command.

  • Looks like Folder Actions have some limitations (and are hard to test without OSX), but watchmedo is working perfectly for me. Thanks! Jun 4 '12 at 23:53

I've tweaked some Ruby scripts I've come across to do exactly what you're looking for. Here's the Ruby code:

# Inspired by http://vikhyat.net/code/snippets/#watchfile

# How to use:
# This script takes two paramaters:  a folder and a shell command
# The script watches for when files in the folder are changed.  When they are, the shell command executes
# Here are some shortcuts you can put in the shell script:
# %F = filename (with extension)
# %B = base filename (without extension)

unless ARGV.length == 2
  puts "\e[32m    Usage: \e[0mruby OnSaveFolder.rb 'folder' 'command'"

require 'digest/md5'
require 'ftools'

$md5 = ''
$directory = File.expand_path(ARGV[0])
$contents = `ls #{$directory}`
$contentsList = $contents.split("\n")
$fileList = []


for i in $contentsList
  if ( File.file?(File.expand_path(i)) == true)

$processes = []

def watch(file, timeout, &cb)
  $md5 = Digest::MD5.hexdigest(File.read(file))
  loop do
    sleep timeout
    if ( temp = Digest::MD5.hexdigest(File.read(file)) ) != $md5
      $md5 = temp

puts "\e[31m Watching files in folder \e[34m #{$directory}"
puts "\e[32m    Press Control+C to stop \e[0m"

for i in $fileList
  pid = fork do
    $num = 0
    $filePath = File.expand_path(i)

    watch i, 1 do |file|
      puts "\n     #{i} saved"

      $command = ARGV[1].dup
      if ( ARGV[1].include?('%F') )
        $command = $command.gsub!('%F', i)
      if ( ARGV[1].include?('%B') )
        $command = $command.gsub!('%B', File.basename(i, '.*'))

      $output = `#{$command}`
      if ( $output != '')
        puts "\e[34m     #{$command}\e[31m output: \e[0m"
        puts $output
      puts "\e[34m     #{$command}\e[31m finished \e[0m (#{$num}, #{Time.now})\n"
      $num += 1



for i in $processes
  `kill #{i}`

I named this script "OnSaveFolder.rb". It takes two parameters: the folder you want to watch for changes, and the bash code you want to run when there's been a change. For example,

ruby OnSaveFolder.rb '/home/Movies' 'echo "A movie has been changed!"'

I hope this helps! I've found that ruby works very well for this type of thing, and it's installed on OS X by default.

  • Gave it a shot but a little hard to tweak without any Ruby background. Thanks anyway! Jun 4 '12 at 23:54
  • this is great. any idea how to make it recursively watch folders below ?
    – Nate Flink
    Jul 10 '13 at 19:35
  • If I don't care about the execution of the command on change, would this be multi-platform, or only unix? And is it actually real time? Some file watchers out there has a ridiculous delay (minutes).
    – Automatico
    Dec 9 '13 at 11:47

You could put lsof into a watch command and have it update every <s> seconds:

watch -n <s> lsof

and launch that with whatever filter, such as watching pid1, pid2, pid3 and ignoring pid4

lsof -p "pid1,pid2,pid3,^pid4"

If that's not enough, you could always write your own filters with grep.

For OS X, see this question's answers.


entr is nice. You can filter the exact files you want it to watch, like this.

find . -name '*.py' | entr python runTests.py

If you want it to only monitor certain files inside a directory, you can craft your find command so that it only returns the files you want to watch.

I find it easier to configure than fswatch.

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