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I want a quick and simple way to execute a command whenever a file changes. I want something very simple, something I will leave running on a terminal and close it whenever I'm finished working with that file.

Currently, I'm using this:

while read; do ./myfile.py ; done

And then I need to go to that terminal and press Enter, whenever I save that file on my editor. What I want is something like this:

while sleep_until_file_has_changed myfile.py ; do ./myfile.py ; done

Or any other solution as easy as that.

BTW: I'm using Vim, and I know I can add an autocommand to run something on BufWrite, but this is not the kind of solution I want now.

Update: I want something simple, discardable if possible. What's more, I want something to run in a terminal because I want to see the program output (I want to see error messages).

About the answers: Thanks for all your answers! All of them are very good, and each one takes a very different approach from the others. Since I need to accept only one, I'm accepting the one that I've actually used (it was simple, quick and easy-to-remember), even though I know it is not the most elegant.

share|improve this question
    
Possible cross site duplicate of: stackoverflow.com/questions/2972765/… ( although here it is on topic =) ) – Ciro Santilli 巴拿馬文件 六四事件 法轮功 Mar 11 '14 at 17:31
    
i've referenced before a cross site duplicate and it was denied :S ;) – Francisco Tapia Sep 9 '15 at 19:51
2  
The solution by Jonathan Hartley builds on other solutions here and fixes big problems that the top-voted answers have: missing some modifications and being inefficient. Please change the accepted answer to his, which also is being maintained on github at github.com/tartley/rerun2 (or to some other solution without those flaws) – nealmcb Nov 23 '15 at 16:12

27 Answers 27

up vote 219 down vote accepted

Simple, using inotifywait (install your distribution's inotify-tools package):

while inotifywait -e close_write myfile.py; do ./myfile.py; done

or

inotifywait -q -m -e close_write myfile.py |
while read -r filename event; do
  ./myfile.py         # or "./$filename"
done

The first snippet is simpler, but it has a significant downside: it will miss changes performed while inotifywait isn't running (in particular while myfile is running). The second snippet doesn't have this defect. However, beware that it assumes that the file name doesn't contain whitespace. If that's a problem, use the --format option to change the output to not include the file name:

inotifywait -q -m -e close_write --format %e myfile.py |
while read events; do
  ./myfile.py
done

Either way, there is a limitation: if some program replaces myfile.py with a different file, rather than writing to the existing myfile, inotifywait will die. Many editors work that way.

To overcome this limitation, use inotifywait on the directory:

inotifywait -e close_write,moved_to,create  . |
while read -r directory events filename; do
  if [ "$filename" = "myfile.py" ]; then
    ./myfile.py
  fi
done

Alternatively, use another tool that uses the same underlying functionality, such as incron (lets you register events when a file is modified) or fswatch (a tool that also works on many other Unix variants, using each variant's analog of Linux's inotify).

share|improve this answer
36  
I've encapsulated all of this (with quite a few bash tricks) in a simple-to-use sleep_until_modified.sh script, available at: bitbucket.org/denilsonsa/small_scripts/src – Denilson Sá Aug 30 '10 at 0:57
10  
while sleep_until_modified.sh derivation.tex ; do latexmk -pdf derivation.tex ; done is fantastic. Thank you. – Rhys Ulerich Dec 15 '11 at 16:49
1  
inotifywait does not play well with temporary files. If you save a file with vim (:w) you'll get 2 CREATE and DELETE signals, as well as 2 MOVE signals. stackoverflow.com/questions/10527936/… – puk May 10 '12 at 22:30
5  
inotifywait -e delete_self seems to work well for me. – Kos Oct 1 '13 at 11:29
3  
It's simple but has two important issues: Events may be missed (all events in the loop) and initialization of inotifywait is done each time which makes this solution slower for large recursive folders. – Wernight Apr 29 '14 at 13:00

I wrote a Python program to do exactly this called when-changed.

Usage is simple:

when-changed FILE COMMAND...

Or to watch multiple files:

when-changed FILE [FILE ...] -c COMMAND

FILE can be a directory. Watch recursively with -r. Use %f to pass the filename to the command.

share|improve this answer
1  
@ysangkok yes it does, in the latest version of the code :) – joh Oct 11 '12 at 16:35
3  
Now available from "pip install when-changed". Still works nicely. Thanks. – A. L. Flanagan Jan 8 '15 at 18:37
2  
To clear the screen first you can use when-changed FILE 'clear; COMMAND'. – Dave James Miller Feb 14 '15 at 9:29
1  
This answer is so much better because I can do it on Windows, too. And this guy actually wrote a program to get the answer. – Wolfpack'08 May 13 '15 at 15:33
1  
Good news everyone! when-changed is now cross-platform! Check out the latest 0.3.0 release :) – joh Jan 23 at 2:41

entr (http://entrproject.org/) provides a more friendly interface to inotify (and also supports *BSD & Mac OS X).

It makes it very easy to specify multiple files to watch (limited only by ulimit -n), takes the hassle out of dealing with files being replaced, and requires less bash syntax:

$ find . -name '*.py' | entr ./myfile.py

I've been using it on my entire project source tree to run the unit tests for the code I'm currently modifying, and it's been a huge boost to my workflow already.

As of May 2014 it's still in active development, with new flags like -c (clear the screen between runs) and -d (exit when a new file is added to a monitored directory).

entr can now also be found in in Debian Jessie/Sid, although it's not got the -d flag there yet. (Building from the author's repo was pain-free anyway.)

share|improve this answer
3  
that works great and seems to be actively maintained. – nikola Mar 10 '14 at 14:28
    
Doesn't handle new files and their modifications. – Wernight Apr 29 '14 at 12:58
    
@Wernight - as of 7th May 2014 entr has the new -d flag; it's slightly more long-winded, but you can do while sleep 1 ; do find . -name '*.py' | entr -d ./myfile.py ; done to deal with new files. – Paul Fenney May 23 '14 at 8:27
1  
available in aur aur.archlinux.org/packages/entr – Victor Häggqvist Jul 1 '15 at 16:33
1  
entr is also available in debian repos at least from debian jessie/8.2 on... – Peter V. Mørch Oct 18 '15 at 21:59

How about this script? It uses the stat command to get the access time of a file and runs a command whenever there is a change in the access time (whenever file is accessed).

#!/bin/bash

### Set initial time of file
LTIME=`stat -c %Z /path/to/the/file.txt`

while true    
do
   ATIME=`stat -c %Z /path/to/the/file.txt`

   if [[ "$ATIME" != "$LTIME" ]]
   then    
       echo "RUN COMMNAD"
       LTIME=$ATIME
   fi
   sleep 5
done
share|improve this answer
5  
Bonus points for simplicity and using basic build-in unix tools :) – CJBrew Oct 18 '13 at 10:54
    
Wouldn't stat-ing the modified time be a better "whenever a file changes" answer? – Xen2050 Feb 27 at 16:42

Solution using Vim:

:au BufWritePost myfile.py :silent !./myfile.py

But I don't want this solution because it's kinda annoying to type, it's a bit hard to remember what to type, exactly, and it's a bit difficult to undo its effects (need to run :au! BufWritePost myfile.py). In addition, this solution blocks Vim until the command has finished executing.

I've added this solution here just for completeness, as it might help other people.

To display the program output (and completely disrupt your editting flow, as the output will write over your editor for a few seconds, until you press Enter), remove the :silent command.

share|improve this answer
    
This can be quite nice when combined with entr (see below) - just make vim touch a dummy file that entr is watching, and let entr do the rest in the background... or tmux send-keys if you happen to be in such an environment :) – Paul Fenney May 23 '14 at 8:42

If you happen to have npm installed, nodemon is probably the easiest way to get started, especially on OS X, which apparently doesn't have inotify tools. It supports running a command when a folder changes.

share|improve this answer
3  
However, it only watches .js and .coffee files. – cormacrelf Jul 20 '12 at 10:27
4  
The current version seems to support any command, for example: nodemon -x "bundle exec rspec" spec/models/model_spec.rb -w app/models -w spec/models – kek Apr 10 '13 at 15:15
    
I didn't know nodemon was this awesome, thank you – pyeleven Oct 24 '13 at 18:38
1  
I wish I had more info, but osx does have a method to track changes, fsevents – ConstantineK Oct 7 '14 at 4:34
1  
On OS X you can also use Launch Daemons with a WatchPaths key as shown in my link. – Adam Johns Nov 16 '14 at 23:48

Here's a simple shell Bourne shell script that:

  1. Takes two arguments: the file to be monitored and a command (with arguments, if necessary)
  2. Copies the file you are monitoring to the /tmp directory
  3. Checks every two seconds to see if the file you are monitoring is newer than the copy
  4. If it's newer it overwrites the copy with the newer original and executes the command
  5. Cleans up after itself when you press Ctr-C

    #!/bin/sh  
    f=$1  
    shift  
    cmd=$*  
    tmpf="`mktemp /tmp/onchange.XXXXX`"  
    cp "$f" "$tmpf"  
    trap "rm $tmpf; exit 1" 2  
    while : ; do  
        if [ "$f" -nt "$tmpf" ]; then  
            cp "$f" "$tmpf"  
            $cmd  
        fi  
        sleep 2  
    done  
    

This works on FreeBSD. The only portability issue I can think of is if some other Unix doesn't have the mktemp(1) command, but in that case you can just hard code the temp file name.

share|improve this answer
7  
Polling is the only portable way, but most systems have a file change notification mechanism (inotify on Linux, kqueue on FreeBSD, ...). You have a severe quoting problem when you do $cmd, but fortunately that's easily fixable: ditch the cmd variable and execute "$@". Your script is not suitable for monitoring a large file, but that could be fixed by replacing cp by touch -r (you only need the date, not the contents). Portability-wise, the -nt test requires bash, ksh or zsh. – Gilles Aug 27 '10 at 22:22

Have a look at incron. It's similar to cron, but uses inotify events instead of time.

share|improve this answer
    
This can be made to work, but creating an incron entry is quite a labour intensive process compared to other solutions on this page. – Jonathan Hartley Sep 9 '15 at 20:37

rerun2 (on github) is a 10-line Bash script of the form:

#!/usr/bin/env bash

function execute() {
    clear
    echo "$@"
    eval "$@"
}

execute "$@"

inotifywait --quiet --recursive --monitor --event modify --format "%w%f" . \
| while read change; do
    execute "$@"
done

Save the github version as 'rerun' on your PATH, and invoke it using:

rerun COMMAND

It runs COMMAND every time there's a filesystem modify event within your current directory (recursive.)

Things one might like about it:

  • It uses inotify, so is more responsive than polling. Fabulous for running sub-millisecond unit tests, or rendering graphviz dot files, every time you hit 'save'.
  • Because it's so fast, you don't have to bother telling it to ignore large subdirs (like node_modules) just for performance reasons.
  • It's extra super responsive, because it only calls inotifywait once, on startup, instead of running it, and incurring the expensive hit of establishing watches, on every iteration.
  • It's just 12 lines of Bash
  • Because it's Bash, it interprets commands you pass it exactly as if you had typed them at a Bash prompt. (Presumably this is less cool if you use another shell.)
  • It doesn't lose events that happen while COMMAND is executing, unlike most of the other inotify solutions on this page.
  • On the first event, it enters a 'dead period' for 0.15 seconds, during which other events are ignored, before COMMAND is run exactly once. This is so that the flurry of events caused by the create-write-move dance which Vi or Emacs does when saving a buffer don't cause multiple laborious executions of a possibly slow-running test suite. Any events which then occur while COMMAND is executing are not ignored - they will cause a second dead period and subsequent execution.

Things one might dislike about it:

  • It uses inotify, so won't work outside of Linuxland.
  • Because it uses inotify, it will barf on trying to watch directories containing more files than the max number of user inotify watches. By default, this seems to be set to around 5,000 to 8,000 on different machines I use, but is easy to increase. See http://unix.stackexchange.com/questions/13751/kernel-inotify-watch-limit-reached
  • It fails to execute commands containing Bash aliases. I could swear that this used to work. In principle, because this is Bash, not executing COMMAND in a subshell, I'd expect this to work. I'd love to hear If anyone knows why it doesn't. Many of the other solutions on this page can't execute such commands either.
  • Personally I wish I was able to hit a key in the terminal it's running in to manually cause an extra execution of COMMAND. Could I add this somehow, simply? A concurrently running 'while read -n1' loop which also calls execute?
  • Right now I've coded it to clear the terminal and print the executed COMMAND on each iteration. Some folks might like to add command-line flags to turn things like this off, etc. But this would increase size and complexity many-fold.

This is a refinement of @cychoi's anwer.

share|improve this answer
    
I believe you should use "$@" instead of $@, in order to properly work with arguments containing spaces. But at the same time you use eval, which forces the user of rerun to be extra careful when quoting. – Denilson Sá Sep 10 '15 at 15:20
    
Thanks Denilson. Could you given an example of where quoting needs to be done carefully? I've been using it the last 24 hours and haven't seen any problems with spaces thus far, nor carefully quoted anything - just invoked as rerun 'command'. Are you just saying that if I used "$@", then the user could invoke as rerun command (without quotes?) That doesn't seem as useful for me: I generally don't want Bash to do any processing of command before passing it to rerun. e.g. if command contains "echo $myvar", then I'll want to see the new values of myvar in each iteration. – Jonathan Hartley Sep 11 '15 at 17:53
    
Something like rerun foo "Some File" might break. But since you are using eval, it can be rewritten as rerun 'foo "Some File". Note that sometimes the path expansion might introduce spaces: rerun touch *.foo will likely break, and using rerun 'touch *.foo' has slightly different semantics (path expansion happening only once, or multiple times). – Denilson Sá Sep 11 '15 at 23:07
    
Thanks for the help. Yep: rerun ls "some file" breaks because of the spaces. rerun touch *.foo* works fine usually, but fails if the filenames that match *.foo contain spaces. Thanks for helping me see how rerun 'touch *.foo' has different semantics, but I suspect the version with single quotes is the semantic I want: I want each iteration of rerun to act as if I typed the command over again - hence I want *.foo to be expanded on each iteration. I'll try your suggestions to examine their effects... – Jonathan Hartley Sep 12 '15 at 5:52
    
More discussion on this PR (github.com/tartley/rerun2/pull/1) and others. – Jonathan Hartley Sep 12 '15 at 6:09

If your program generates some sort of log/output, you can create a Makefile with a rule for that log/output that depends on your script and do something like

while true; do make -s my_target; sleep 1; done

Alternately, you can create a phony target and have the rule for it both call your script and touch the phony target (while still depending on your script).

share|improve this answer
11  
while sleep 1 ; do something ; done is slightly better than while true ; do something ; sleep 1 ; done. At least it stops easily when pressing Ctrl+C. – Denilson Sá Aug 28 '10 at 4:59
    
Will removing the sleep cause a busy loop (CPU generating heat and hurting battery life on a laptop)? – Steven Lu Jul 12 '12 at 4:52
1  
@StevenLu: no, the sleep is not a busy wait. The problem is that if the sleep is in the body, Control-C will kill the sleep and the loop will start over. Power usage of starting the loop over is insignificant. Try it yourself in a terminal. You need to hold Control-C for it to work, if you have sleep in the body. – Janus Troelsen Sep 19 '12 at 11:25
    
Right. I think I missed it and didn't see that the sleep is still present as the loop condition. That little tweak is pretty awesome. – Steven Lu Sep 19 '12 at 17:55

Another solution with NodeJs, fsmonitor :

  1. Install

    sudo npm install -g fsmonitor
    
  2. From command line (example, monitor logs and "retail" if one log file change)

    fsmonitor -s -p '+*.log' sh -c "clear; tail -q *.log"
    
share|improve this answer
    
Side note: the example could be solved by tail -F -q *.log, I think. – Volker Siegel Apr 18 '15 at 1:39

Look into Guard, in particular with this plugin:

https://github.com/hawx/guard-shell

You can set it up to watch any number of patterns in your project's directory, and execute commands when changes occur. Good chance even that there's a plugin available for that what you're trying to do in the first place.

share|improve this answer

Under Linux:

man watch

watch -n 2 your_command_to_run

Will run the command every 2 seconds.

If your command takes more than 2 seconds to run, watch will wait until it's done before doing it again.

share|improve this answer
    
That's pretty simple, though somewhat of a waste, it's easy for development tasks like making live changes to styles. – Xeoncross Jul 15 '14 at 18:32
1  
What happens when the command takes longer than two seconds to run? – thirtythreeforty Feb 24 '15 at 6:53
    
@thirtythreeforty A quick experiment on Ubuntu shows that watch will wait the full two seconds no matter how long the command takes to run. FWIW, the sleep period can be specified with '-n', down to a minimum of 0.1 seconds. – Jonathan Hartley Sep 9 '15 at 20:36

For those of you who are looking for a FreeBSD solution, here is the port:

/usr/ports/sysutils/wait_on
share|improve this answer

if you have nodemon installed, then you can do this:

nodemon -w <watch directory> -x "<shell command>" -e ".html"

In my case I edit html locally and ship it to my remote server when a file changes.

nodemon -w <watch directory> -x "scp filename jaym@jay-remote.com:/var/www" -e ".html"
share|improve this answer

swarminglogic wrote a script called watchfile.sh, also available as a GitHub Gist.

share|improve this answer
    
Excellent find. Thanks – Ibn Saeed Apr 21 '15 at 8:00
    
This is a feature-packed 200 line Bash script that polls stat on the given filenames, runs md5sum on the output, and re-runs the given command if this value changes. Because it's Bash, I suspect it does a good job of running the given command exactly as if you typed it at a Bash prompt. (In contrast, most of the solutions here written in other languages will fail to execute commands which, for example, contain shell aliases such as ll) – Jonathan Hartley Sep 9 '15 at 20:30

Improved upon Gilles's answer.

This version runs inotifywait once and monitors for events (.e.g.: modify) thereafter. Such that inotifywait doesn't need to be re-executed upon every event encountered.

It's quick and fast!(even when monitoring large directory recursively)

inotifywait --quiet --monitor --event modify FILE | while read; do
    # trim the trailing space from inotifywait output
    REPLY=${REPLY% }
    filename=${REPLY%% *}
    # do whatever you want with the $filename
done
share|improve this answer
    
This is the best answer on the page for Linux-only users. Replace the stuff inside the loop with 'execute $@', and the user could call this script passing in their own command to run. It even works with commands that contain shell aliases if you source it, using something like ". scriptname COMMAND". This will still find scriptname on the PATH. – Jonathan Hartley Sep 9 '15 at 21:00
    
I think you mean to put 'while read REPLY' ? – Jonathan Hartley Sep 9 '15 at 21:00
1  
I rolled these fixes up into an anwer of my own: search this page for 'rerun2' – Jonathan Hartley Sep 9 '15 at 21:50
    
By Reading The Fu*king Manual, namely help read, If no NAMEs are supplied, the line read is stored in the REPLY variable.. – cychoi Sep 25 '15 at 23:40
    
thanks for the clarification. Unthanks for the phasing of it! I would have deleted those comments, but of course now I won't. – Jonathan Hartley Sep 30 '15 at 11:25

A little more on the programming side, but you want something like inotify. There are implementations in many languages, such as jnotify and pyinotify.

This library allows you to monitor single files or entire directories, and returns events when an action is discovered. The information returned includes the file name, the action (create, modify, rename, delete) and the file path, among other useful information.

share|improve this answer

I like the simplicity of while inotifywait ...; do ...; done however it has two issues:

  • File changes happening during the do ...; will be missed
  • Slow when using in recursive mode

Therefor I made a helper script that uses inotifywait without those limitations: inotifyexec

I suggest you put this script in your path, like in ~/bin/. Usage is described by just running the command.

Example: inotifyexec "echo test" -r .

share|improve this answer
    
Updated the script to support regex pattern matching. – Wernight Oct 21 '14 at 12:56
    
Both problems are solved by using inotifywait in "--monitor" mode. See cychoi's answer. – Jonathan Hartley Sep 9 '15 at 20:01

Watchdog is a Python project, and may be just what you're looking for:

Supported platforms

  • Linux 2.6 (inotify)
  • Mac OS X (FSEvents, kqueue)
  • FreeBSD/BSD (kqueue)
  • Windows (ReadDirectoryChangesW with I/O completion ports; ReadDirectoryChangesW worker threads)
  • OS-independent (polling the disk for directory snapshots and comparing them periodically; slow and not recommended)

Just wrote a command-line wrapper for it watchdog_exec:

Example runs

On fs event involving files and folders in current directory, run echo $src $dst command, unless it the fs event is modified, then run python $src command.

python -m watchdog_exec . --execute echo --modified python

Using short arguments, and restricting to only execute when events involve "main.py":

python -m watchdog_exec . -e echo -a echo -s __main__.py

EDIT: Just found Watchdog has an official CLI called watchmedo, so check that out also.

share|improve this answer

I use this script to do it. I'm using inotify in monitor-mode

#!/bin/bash
MONDIR=$(dirname $1)
ARQ=$(basename $1)

inotifywait -mr -e close_write $MONDIR | while read base event file 
do
  if (echo $file |grep -i "$ARQ") ; then
    $1
  fi
done

Save this as runatwrite.sh

Usage: runatwrite.sh myfile.sh

it will run myfile.sh at each write.

share|improve this answer

Improved Sebastian's solution with watch command:

watch_cmd.sh:

#!/bin/bash
WATCH_COMMAND=${1}
COMMAND=${2}

while true; do
  watch -d -g "${WATCH_COMMAND}"
  ${COMMAND}
  sleep 1     # to allow break script by Ctrl+c
done

Call example:

watch_cmd.sh "ls -lR /etc/nginx | grep .conf$" "sudo service nginx reload"

It works but be careful: watch command has known bugs (see man): it reacts on changes only in VISIBLE in terminal parts of -g CMD output.

share|improve this answer

For people who find this by Googling for changes to a particular file, the answer is much simpler (inspired by Gilles's answer).

If you want to do something after a particular file has been written to, here's how:

while true; do
  inotifywait -e modify /path/to/file
  # Do something *after* a write occurs, e.g. copy the file
  /bin/cp /path/to/file /new/path
done

Save this as, for example, copy_myfile.sh and put the .sh file into the /etc/init.d/ folder to have it run on startup.

share|improve this answer
    
Shares the problem with Giles' answer that it runs inotifywait on every iteration, which can be unresponsive for recursively watching very large directories. See cychoi's answer for the fix to this. – Jonathan Hartley Sep 9 '15 at 19:51

A oneliner answer that I'm using to keep track on a file change:

$ while true ; do NX=`stat -c %Z file` ; [[ $BF != $NX ]] && date >> ~/tmp/fchg && BF=$NX || sleep 2 ; done

You don't need to initialize BF if you know that the first date is the starting time.

This is simple and portable. There is another answer based on the same strategy using a script here. Take a look also.


Usage: I'm using this to debug and keep an eye on ~/.kde/share/config/plasma-desktop-appletsrc; that for some unknown reason keeps loosing my SwitchTabsOnHover=false

share|improve this answer

I wrote a Python program to do exactly this, called rerun.

UPDATE: This answer is not remotely as good as my other answer, search this page for 'rerun2'.

Install with:

pip install rerun

and usage is very simple:

rerun "COMMAND"

The command is expected as a single arg, not a sequence of space-separated args. Hence quote it as shown, which reduces any extra escaping you'd have to add. Just type the command as you would have typed it at the command line, but surrounded by quotes.

By default it watches all files in or under the current directory, skipping things like known source control dirs, .git, .svn, etc.

Optional flags include '-i NAME' which ignores changes to named files or directories. This can be given multiple times.

Since it's a Python script, it needs to run the command as a sub-process, and we use a new instance of the user's current shell to interpret 'COMMAND' and decide what process to actually run. However, if your command contains shell aliases and the like which are defined in .bashrc, these will not be loaded by the subshell. To fix this, you can give rerun a '-I' flag, to use interactive (aka 'login') subshells. This is slower and more error-prone than starting a regular shell, because it has to source your .bashrc.

I use it with Python 3, but last I checked rerun still worked with Python 2.

Double-edged sword is that it uses polling instead of inotify. On the upside, this means it works on every OS. Plus, it's better than some other solutions shown here in terms of only running the given command once for a bunch of filesystem changes, not once per modified file, while at the same time it does run the command a second time if any files change again while command is running.

On the downside, polling means that there is a 0.0 to 1.0 second latency, and of course it's slow to monitor extremely large directories. Having said that, I've never encountered a project large enough that this is even noticeable so long as you use '-i' to ignore big things like your virtualenv and node_modules.

Hmmm. rerun has been indispensible to me for years - I basically use it eight hours every day for running tests, rebuilding dot files as I edit them, etc. But now I come to type this up here, it's clear that I need to switch to a solution that uses inotify (I no longer use Windows or OSX.) and is written in Bash (so it works with aliases without any extra fiddling.)

share|improve this answer
    
This answer is not remotely as good as my other answer (rerun2) – Jonathan Hartley Sep 9 '15 at 21:50

For those who can't install inotify-tools like me, this should be useful:

watch -d -t -g ls -lR

This command will exit when the output changes, ls -lR will list every file and directory with its size and dates, so if a file is changed it should exit the command, as man says:

-g, --chgexit
          Exit when the output of command changes.

I know this answer may not be read by anyone, but I hope someone would reach to it.

Command line example:

~ $ cd /tmp
~ $ watch -d -t -g ls -lR && echo "1,2,3"

Open another terminal:

~ $ echo "testing" > /tmp/test

Now the first terminal will output 1,2,3

Simple script example:

#!/bin/bash
DIR_TO_WATCH=${1}
COMMAND=${2}

watch -d -t -g ls -lR ${DIR_TO_WATCH} && ${COMMAND}
share|improve this answer

For those using OS X, you can use a LaunchAgent to watch a path/file for changes and do something when that happens. FYI - LaunchControl is a good app to easily make/modify/remove daemons/agents.

(example taken from here)

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC -//Apple Computer//DTD PLIST 1.0//EN
http://www.apple.com/DTDs/PropertyList-1.0.dtd>
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>test</string>
    <key>ProgramArguments</key>
    <array>
        <string>say</string>
        <string>yy</string>
    </array>
    <key>WatchPaths</key>
    <array>
        <string>~/Desktop/</string>
    </array>
</dict>
</plist>
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