Using a shell script, can I watch a folder and block program execution until a file in a certain folder changes?
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.
The simplest solution is entr, I use it a lot for development - https://www.linuxbash.sh/post/entr-rerun-commands-when-files-change
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.
As another commenter said, you want inotifywait:
Maybe inotify or one of those “watcher” (not “watch”) tools available, but I don’t remember which one to use.
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 }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 30in it. Adjust numbers to your desired tolerance.Again, don’t do that. But if you must, definitely don’t do an md5sum for godssake.
The fuck…
Oh god please don’t do this. Constantly reading the file is just stressing your IO for no reason.
Please inotify instead:
I really like this, replace compile with whatever command you desire I guess.
This is a terrible solution. You will stress your IO for no reason.
On the upside, you do not need to install the
inotifywaitpackage.md5sumalready installed on my system hahaIt isn’t a terrible solution if you are checking infrequently just as ever 30 minutes.
why is that a plus
I do not need to install anything/can work on bare install without internet connection?
ah, fair.
You should be able to tie into the kernel with some C programming if you want to go extra small.
If you are a big fan of wasting disk performance, CPU cycles, and ultimately power.
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.
There is inotifywait which seems to do the job, The Wiki
