I want a script to sleep unless a certain file is modifed/deleted (or a file created in a certain directory, or ...). Can this be achieved in some elegant way? The simplest thing that comes to my mind is a loop that sleeps for some time before checking the status again, but maybe there is a more elegant way?


3 Answers 3


On linux, you can use the kernel's inotify feature. Tools for scripting can be found there: inotify-tools.

Example use from wiki:


EVENT=$(inotifywait --format '%e' ~/file1) # blocking without looping
[ $? != 0 ] && exit
[ "$EVENT" = "MODIFY" ] && echo 'file modified!'
[ "$EVENT" = "DELETE_SELF" ] && echo 'file deleted!'
# etc...
  • 1
    Most unices have a similar feature. Unfortunately each has its own interface, and many have no shell API. Jan 7, 2011 at 18:40

There is an API called inotify for C programmers.

There are some tools that use it, e.g. incron and inotify-tools.

  • Tremendous, that’s the stuff. Cheers Mikel! Apr 6, 2011 at 8:52

Indeed there is: entr(1) will run arbitrary commands when files change, and also provides an auto-reload option for restarting application servers.

edit: some examples

Rebuild if sources files change

$ find *.c | entr make

Launch and auto-reload test server if files change

$ ls *.py | entr -r python main.py

Providing a the agument +/path/to/fifo allows more complex scripting by instructing entr to write the name of each file that changes to a named pipe. The following will convert Markdown files in the current directory to HTML as they're edited

$ ls *.md | entr +/tmp/notify &
$ while read F
> do
>   markdown2html $F
> done < /tmp/notify
  • Intriguing, but weird. So ... it reads a bunch of file names on standard input, and runs the specified command when one of them changes?
    – tripleee
    Jul 4, 2013 at 5:36
  • Looks interesting, thanks! Is there any way to have entr pass on the name of the file that has changed as well? Jul 4, 2013 at 7:00
  • As of the 2.7 release, the special /_ argument (somewhat analogous to $_ in Perl) is replaced with the name of the first file that changed
    – eradman
    Dec 6, 2014 at 11:50
  • @TobiasKienzler also, maybe you could use xargs -I % entr <command> % to pass the file name from the previous pipe of find *.ext | or use the special argument as @eradman suggests
    – alchemy
    Feb 12, 2022 at 22:50

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