====== BASH - Directories - Monitor a directory for changes - Using inotifywait ======

===== Install inotify-tools =====

<code bash>
sudo apt install inotify-tools
</code>

----

===== Test inotifywait =====

In a shell enter:

<code bash>
while true; do
  res=`inotifywait -r thedirtowatch/ --format %f`;
  echo "RESULT=$res";
done
</code>

returns:

<code>
Setting up watches.  Beware: since -r was given, this may take a while!
Watches established.
</code>

<WRAP info>
**NOTE:**  The **<nowiki>--format %f</nowiki>** refers to the filename in the event.

  * **<nowiki>-r, --recursive</nowiki>**:  Watch all sub-directories of any directories passed as arguments.   Watches will be set up recursively to an unlimited depth.   
    * Symbolic links are not traversed.  Newly created sub-directories will also be watched.


See http://manpages.ubuntu.com/manpages/focal/man1/inotifywait.1.html for options.
</WRAP>


----

In a 2nd shell, go to that directory being watched.

<code bash>
cd thedirtowatch/
touch test1
</code>

<WRAP info>
**NOTE:**  Back on the 1st shell this should show you output:

<code bash>
RESULT=test1
</code>
</WRAP>


----

===== Only listen for certain events =====

Change the inotifywait to the following:

<code bash>
while true; do
  res=`inotifywait -q -e create, open, close, modify, moved_to, moved_from -r thedirtowatch/ --format '%e %f'`;
  echo "RESULT=$res\n";
done
</code>


<WRAP info>
**NOTE:**  The additional **-e** option can be added to the inotifywait to only listen for certain events.

Events include:

  * **access**: A watched file or a file within a watched directory was read from.
  * **modify**: A watched file or a file within a watched directory was written to.
  * **attrib**: The  metadata  of a watched file or a file within a watched directory was modified.
    * This includes timestamps, file permissions, extended attributes etc.
  * **close_write**: A watched file or a file within a watched directory was closed, after being opened in writeable mode.
    * This does not necessarily imply the file was written to.
  * **close_nowrite**:  A watched file or a file within a watched directory was closed, after being opened in read-only mode.
  * **close**:  A watched file or a file within a watched directory was closed, regardless of how it was opened.
    * Note that this is actually implemented simply by listening for both **close_write** and **close_nowrite**, hence all close events received will be output as one of these, not **CLOSE**.
  * **open**:  A watched file or a file within a watched directory was opened.
  * **moved_to**:  A  file or directory was moved into a watched directory.
    * This event occurs even if the file is simply moved from and to the same directory.
  * **moved_from**:  A file or directory was moved from a watched directory.
    * This event occurs even if the file is simply moved from and to the same directory.
  * **move**:  A file or directory was moved from or to a watched directory.
    * Note that this is actually implemented simply by listening for both **moved_to** and **moved_from**, hence all **close** events received will be output as one or both of these, not **MOVE**.
  * **move_self**:  A watched  file or directory was moved.
    * After this event, the file or directory is no longer being watched.
  * **create**:  A file or directory was created within a watched directory.
  * **delete**:  A file or directory within a watched directory was deleted.
  * **delete_self**:  A watched file or directory was deleted.
    * After this event the file or directory is no longer being watched.
    * Note that this event can occur even if it is not explicitly being listened for.
  * **unmount**:  The filesystem on which a watched file or directory resides was  unmounted.
    * After this event the file or directory is no longer being watched.
    * Note that this event can occur even if it is not explicitly being listened to.

The **<nowiki>--format</nowiki>** option is changed to include showing **%e** which is the actual event.  Obviously change as needed.

The **-q** option is to not show too much output.

See http://manpages.ubuntu.com/manpages/focal/man1/inotifywait.1.html for options.

</WRAP>

----

===== Using monitor mode =====

Instead of running in a **while true; do** loop, an alternative is to use monitor mode:

<code bash>
inotifywait -m thedirtowatch/ -e create -e moved_to |
  while read dir action file; do
    echo "The file '$file' appeared in directory '$dir' via '$action'"
    # do something with the file.
  done
</code>

<WRAP info>
**NOTE:**  The **<nowiki>--format %f</nowiki>** refers to the filename in the event.

  * **<nowiki>-m, --monitor</nowiki>**:  Instead of exiting after receiving a single event, execute indefinitely.
    * The default behavior is to exit after the first event occurs.

See http://manpages.ubuntu.com/manpages/focal/man1/inotifywait.1.html for options.
</WRAP>



----

===== Using a BASH Script =====

<file bash after-change.sh>
#!/bin/bash
#
# Monitor the input directory and if any change occurs run the provided command:
#
# Usage:
#   after-change.sh /tmp ls -al %f

if [ $# -lt 3 ]; then
  echo "Usage: $0 dir cmd "
  exit 1
fi

which inotifywait 2>&1 >/dev/null

if [ "$?" == "1" ]; then
  echo "ERROR:  inotifywait not installed."
  exit 1
fi

dir=$1
shift
cmd=$1
shift
options=$*

inotifywait -q -r -m $dir $options
eval $cmd
</file>

----

===== References =====

http://manpages.ubuntu.com/manpages/focal/man1/inotifywait.1.html