How do I set up cron to run a file just once at a specific time? [closed]

Answer 1

Your comment suggests you're trying to call this from a programming language. If that's the case, can your program fork a child process that calls sleep then does the work?

What about having your program calculate the number of seconds until the desired runtime, and have it call shell_exec("sleep ${secondsToWait) ; myCommandToRun");