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Directory - Run a Command Upon Files or Directories Changes

Use either inotifywait or iwatch.

Using inotifywait

Install inotify-tools

sudo apt install inotify-tools

Test inotifywait

In a shell enter:

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

returns:

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

NOTE: The --format %f refers to the filename in the event.

-r, –recursive: 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.

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

cd thedirtowatch/
touch test1

NOTE: Back on the 1st shell this should show you output:

RESULT=test1

Only listen for certain events

Change the inotifywait to the following:

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

NOTE: The additional -e option can be added to the inotifywait to only listen for certain events.

The --format 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.

Using a BASH Script

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

References

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

Wiki

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