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--- bash:directories:monitor_a_directory_for_changes:using_inotifywait [2022/06/13 09:15] – created peter
+++ bash:directories:monitor_a_directory_for_changes:using_inotifywait [2022/06/13 09:17] (current) – peter
@@ Line 1: / Line 1: @@
 ====== 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