I have written a php script to check if there are any new files in a folder and, if any new files exist, upload them to a server. These files can be quite large. I want to run this script frequently-let's say every 5 min-as a scheduled task so that the files get moved to the server as soon as possible. However, once the script is already attempting to upload a file, I do not want it to be run again, as I am afraid the second instance will overwrite the file that is already being uploaded to the server.
How can I run the script as a scheduled task unless the script is already running?