How to Monitor Newly Created File in a Directory with Bash

Bash script to check if a new file has been created on a directory after run a command

Thanks to informative comments, I've just realized that I've missed the basics of bash script but finally made that work. I'll leave my solution here as an answer for those who struggle like me.:

WATCH_DIR=./tmp

FILES_BEFORE=$(ls $WATCH_DIR)

echo >$WATCH_DIR/filename

FILES_AFTER=$(ls $WATCH_DIR)

if diff <(echo "$FILES_AFTER") <(echo "$FILES_BEFORE")
then
    echo "No changes"
else
    echo "Changes"
fi

It outputs "Changes" on the first run and "No Changes" for the other unless you delete the newly added documents.

Monitor Pre-existing and new files in a directory with bash

Once inotifywait is up and waiting, it will print the message Watches established. to standard error. So you need to go through existing files after that point.

So, one approach is to write something that will process standard error, and when it sees that message, lists all the existing files. You can wrap that functionality in a function for convenience:

function list-existing-and-follow-modify() {
  local path="$1"
  inotifywait --monitor \
              --event modify \
              --format %f \
              -- \
              "$path" \
    2> >( while IFS= read -r line ; do
            printf '%s\n' "$line" >&2
            if [[ "$line" = 'Watches established.' ]] ; then
              for file in "$path"/* ; do
                if [[ -e "$file" ]] ; then
                  basename "$file"
                fi
              done
              break
            fi
          done
          cat >&2
        )
}

and then write:

list-existing-and-follow-modify "$path" \
| while IFS= read -r file
    # ... work on/with "$file"
    # move "$file" to a new directory
  done

Notes:

• If you're not familiar with the >(...) notation that I used, it's called "process substitution"; see https://www.gnu.org/software/bash/manual/bash.html#Process-Substitution for details.
• The above will now have the opposite race condition from your original one: if a file is created shortly after inotifywait starts up, then list-existing-and-follow-modify may list it twice. But you can easily handle that inside your while-loop by using if [[ -e "$file" ]] to make sure the file still exists before you operate on it.
• I'm a bit skeptical that your inotifywait options are really quite what you want; modify, in particular, seems like the wrong event. But I'm sure you can adjust them as needed. The only change I've made above, other than switching to long options for clarity/explicitly and adding -- for robustness, is to add --format %f so that you get the filenames without extraneous details.
• There doesn't seem to be any way to tell inotifywait to use a separator other than newlines, so, I just rolled with that. Make sure to avoid filenames that include newlines.

How to track order of newly created files in directory with fswatch

Bash script handle_order.sh that will maintain order in the track_order text file

#!/bin/bash
echo "new file is added $1"
filename=$(basename ${1})
echo $filename
if [ $filename != "track_order.txt"  ]; then
echo "${filename}" >> track_order.txt
else
echo "order is updated"
fi

fswatch command

fswatch ./DRS-1.1.0/ --event Created | xargs -I '{}' sh -c './handle_order.sh "$1"' - {}

• (./DRS-1.1.0/) your directory name which needs to be monitor
• (handle_order.sh) bash script that will handle the order and update track_order.txt file
• (Created) only create an event

Updated:

remove the handle_order.sh and run as a single command

fswatch ./DRS-1.1.0/ --event Created | xargs -I '{}' sh -c 'filename=$(basename ${1});echo $filename;if [ $filename != "track_order.txt"  ]; then echo "${filename}" >> track_order.txt; else echo "order is updated";fi' - {}

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