How may I watch for the creation of a particular "trigger file"?

Question

I need to create a shell script that executes an application when a file called start is created in a particular directory.

How may I write a shell script that waits for the creation of a file with a certain name in a certain location?

Answer 1

If your system has inotifywait (most Linux distributions, OpenBSD and possibly others), as others have mentioned the least resource-intensive approach is to use inotifywait:

rm -f yourdirectory/start
while [ "$(inotifywait -e create -q --format %f yourdirectory)" != "start" ]; do :; done
yourcommand

That will ensure the start file is removed from yourdirectory, then wait for its creation, and then run yourcommand. -e create specifies that we’re only interested in creation events, -q specifies that we don’t want inotifywait’s diagnostic messages, and --format %f specifies that we only want to see the created file’s name in the output.

If you don’t have inotifywait, the following will work too, with a delay of at most one second:

rm -f yourdirectory/start
while [ ! -e yourdirectory/start ]; do sleep 1; done
yourcommand

Answer 2

I like the tool 'inoticoming' for watching a directory for change. has logging and pid-file creation. you can run command on change with additional 'action-options' it's pretty decent :)

i also remember a tool called 'fileschanged' but never got to play with it, could be worth a look. -Jay