How to execute a command whenever a file changes?

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.

376
задан Denilson Sá Maia 0000-00-00 00:00:00
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23 ответов

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 -m . |
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).

357
отвечен Gilles 2017-07-28 09:43:20
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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.

Flags like -c (clear the screen between runs) and -d (exit when a new file is added to a monitored directory) add even more flexibility, for example you can do:

$ while sleep 1 ; do find . -name '*.py' | entr -d ./myfile.py ; done

As of early 2018 it's still in active development and it can be found in Debian & Ubuntu (apt install entr); building from the author's repo was pain-free in any case.

127
отвечен Paul Fenney 2018-04-05 10:58:59
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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.

102
отвечен joh 2013-10-04 13:20:12
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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 COMMAND"
       LTIME=$ATIME
   fi
   sleep 5
done
46
отвечен VDR 2018-05-23 16:56:14
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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.

28
отвечен Denilson Sá Maia 2010-08-28 00:41:11
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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.

24
отвечен davidtbernal 2015-10-25 18:49:04
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rerun2 (on github) is a 10-line Bash script of the form:

#!/usr/bin/env bash

function execute() {
    clear
    echo "[email protected]"
    eval "[email protected]"
}

execute "[email protected]"

inotifywait --quiet --recursive --monitor --event modify --format "%w%f" . \
| while read change; do
    execute "[email protected]"
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 https://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.

13
отвечен Jonathan Hartley 2017-04-13 15:37:10
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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.

12
отвечен MikeyMike 2010-08-28 02:16:22
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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}
9
отвечен Sebastian 2016-03-22 17:57:03
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Have a look at incron. It's similar to cron, but uses inotify events instead of time.

8
отвечен Florian Diesch 2010-08-28 00:12:59
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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"
    
7
отвечен Atika 2014-01-22 19:39:10
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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.

6
отвечен Eric Leschinski 2015-10-25 18:52:02
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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.

5
отвечен Wouter Van Vliet 2014-07-09 17:16:10
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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 [email protected]:/var/www" -e ".html"
5
отвечен Jay 2014-08-09 02:20:09
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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).

4
отвечен ctgPi 2010-08-28 00:37:52
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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
4
отвечен cychoi 2017-03-20 13:17:03
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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.

3
отвечен John T 2010-08-28 00:05:59
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For those of you who are looking for a FreeBSD solution, here is the port:

/usr/ports/sysutils/wait_on
3
отвечен akond 2013-07-17 16:29:52
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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 .

3
отвечен Wernight 2014-05-01 00:39:37
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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.

3
отвечен Samuel Marks 2015-12-28 13:44:18
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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.

3
отвечен alex_1948511 2017-03-20 13:17:25
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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

1
отвечен Dr Beco 2015-09-01 07:53:52
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