Run a shell script whenever a file in a certain directory changes?

After some suggestions to check out inotifywait I ended up with a solution that works for me as desired.

    
inotifywait --event modify,create ./targetfolder/; echo "new change, that I am interested in, occurred in targetfolder";

It turned out I was interested in both file modification and file creation events.

There is inotifywait which seems to do the job, The Wiki

Maybe inotify or one of those "watcher" (not "watch") tools available, but I don't remember which one to use.

The simplest solution is entr, I use it a lot for development - https://www.linuxbash.sh/post/entr-rerun-commands-when-files-change

What is the end goal?

a hobby project: generate a rss feed based on recent file changes in a directory. But I thought this can also have many applications …
auto formatting code files on change
automatic backups of a certain folder: run rsync on change in folder.
- Are you familiar with CI/CD pipelines? You could use Git along with a service like Woodpecker CI or Gitlab Runners.

Can continuously loop over the file, examine the md5 hash for changes.

Run the script if it has changed.

https://stackoverflow.com/questions/6475252/bash-script-watch-folder-execute-command

        daemon() {
    chsum1=""

    while [[ true ]]
    do
        chsum2=`find src/ -type f -exec md5 {} \;`
        if [[ $chsum1 != $chsum2 ]] ; then           
            if [ -n "$chsum1" ]; then
                compile
            fi
            chsum1=$chsum2
        fi
        sleep 2
    done
    }

The fuck…
Even if you wanted to implement a solution like this, which you shouldn't, why on earth monitor the MD5 sum instead of just the mtime of the file???? Like, doing a checksum is the least efficient method of checking this possible.
Like, you could do a simple while loop with a find myfile.txt +mmin 1; sleep 30 in it. Adjust numbers to your desired tolerance.
Again, don't do that. But if you must, definitely don't do an md5sum for godssake.
I really like this, replace compile with whatever command you desire I guess.

Block execution not entirely. You could chmod it as non-x and use inotifywatch to flip it back.

Edit: I misunderstood you, use inotifywait like the other person suggested.