Run a shell script whenever a file in a certain directory changes? (lemmy.ml)

submitted 5 months ago* (last edited 5 months ago) by helloworld@lemmy.ml to c/linuxquestions@lemmy.zip

22 comments fedilink hide all child comments

Using a shell script, can I watch a folder and block program execution until a file in a certain folder changes?

you are viewing a single comment's thread
view the rest of the comments

[-] running_ragged@lemmy.world -2 points 5 months ago

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
}

[-] hperrin@lemmy.ca 15 points 5 months ago

Oh god please don’t do this. Constantly reading the file is just stressing your IO for no reason.

Please inotify instead:

https://linux.die.net/man/1/inotifywait

[-] chonkyninja@lemmy.world 4 points 5 months ago

The fuck…

[-] testfactor@lemmy.world 2 points 5 months ago

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.

[-] helloworld@lemmy.ml -1 points 5 months ago

I really like this, replace compile with whatever command you desire I guess.

[-] hperrin@lemmy.ca 10 points 5 months ago

This is a terrible solution. You will stress your IO for no reason.

[-] helloworld@lemmy.ml 0 points 5 months ago* (last edited 5 months ago)

On the upside, you do not need to install the inotifywait package. md5sum already installed on my system haha

[-] hperrin@lemmy.ca 11 points 5 months ago

If you are a big fan of wasting disk performance, CPU cycles, and ultimately power.

[-] nublug@lemmy.blahaj.zone 2 points 5 months ago

why is that a plus

[-] helloworld@lemmy.ml 1 points 5 months ago

I do not need to install anything/can work on bare install without internet connection?

[-] nublug@lemmy.blahaj.zone 1 points 5 months ago

ah, fair.

[-] possiblylinux127@lemmy.zip 1 points 5 months ago* (last edited 5 months ago)

You should be able to tie into the kernel with some C programming if you want to go extra small.

[-] possiblylinux127@lemmy.zip 2 points 5 months ago

It isn't a terrible solution if you are checking infrequently just as ever 30 minutes.

this post was submitted on 25 Aug 2025

24 points (100.0% liked)

Linux Questions

3653 readers

5 users here now

Linux questions Rules (in addition of the Lemmy.zip rules)

stay on topic
be nice (no name calling)
do not post long blocks of text such as logs
do not delete your posts
only post questions (no information posts)

Tips for giving and receiving help

be as clear and specific
say thank you if a solution works
verify your solutions before posting them as facts.

Any rule violations will result in disciplinary actions

founded 2 years ago

MODERATORS

possiblylinux127@lemmy.zip