As I prepare and run a lot of scripts, sometimes I need to run a script at a precise time of the day.

When a script must be only run once, cron is not a viable solution. So I discovered the at scheduler

You need to install it first, using apt as usual.

$ sudo apt install at

Schedule a command to run

1. use the command at with a time / date
2. input the commands to run in the prompt
3. type CTRL+D to exit (^D)

$ at 9AM       
warning: commands will be executed using /bin/sh
at> cd workspaces/github/dotfiles
at> git pull
at> <EOT>
job 1 at Sat Apr 16 09:00:00 2022

This example will pull a repository contents at 9 AM tomorrow !

at supports a lot of time specifications.

Here is an extract of its man page:

At allows fairly complex time specifications, extending the POSIX.2 standard. It accepts times of the form HH:MM to run a job at a specific time of day. (If that time is already past, the next day is assumed.) You may also specify midnight, noon, or teatime (4pm) and you can have a time-of-day suffixed with AM or PM for running in the morning or the evening.

The commands are executed with the logged-in user account, using a /bin/sh shell. It will use the available env-vars of the shell when the command at is executed, and will cd into the current directory before running your scruipt.

view scheduled commands

$ atq
1	Sat Apr 16 09:00:00 2022 a jwittouck

view the details of a job

$ at -c 1


cd /home/jwittouck || {
	 echo 'Execution directory inaccessible' >&2
	 exit 1
}
cd workspaces/github/dotfiles
git pull

delete a job

$ atrm 1