How to use the command "at" (with examples)

The at command is used to execute commands once at a later time. It requires the atd (or atrun) service to be running for the actual execution of commands.

Use case 1: Execute commands from stdin in 5 minutes

Code:

at now + 5 minutes

Motivation: This use case allows you to schedule the execution of commands from the standard input in 5 minutes. It can be useful when you want to delay the execution of a command.

Explanation:

• at: The command itself.
• now + 5 minutes: Specifies that the command should be executed 5 minutes from the current time.

Example output:

warning: commands will be executed using /bin/sh
at> echo "Hello, world!"
at> <EOT>
job 1 at Tue Jan  4 12:05:00 2022

In this example, the command echo "Hello, world!" was queued to be executed in 5 minutes and a job number (1) is assigned to it.

Use case 2: Execute a command from stdin at 10:00 AM today

Code:

echo "./make_db_backup.sh" | at 1000

Motivation: This use case allows you to schedule the execution of a specific command at a specified time. It can be used to automate tasks, such as backups, that need to be performed at a specific time.

Explanation:

• echo "./make_db_backup.sh" | at 1000: The command echo "./make_db_backup.sh" will output the command to be executed (./make_db_backup.sh) and the pipe (|) sends the output as the standard input to the at command. 1000 specifies the time of execution as 10:00 AM.

Example output:

warning: commands will be executed using /bin/sh
job 2 at Wed Jan  5 10:00:00 2022

In this example, the command ./make_db_backup.sh was scheduled to be executed at 10:00 AM today and a job number (2) is assigned to it.

Use case 3: Execute commands from a given file next Tuesday

Code:

at -f path/to/file 9:30 PM Tue

Motivation: This use case allows you to schedule the execution of commands stored in a file at a specific time. It can be useful when you have a set of commands that need to be executed together.

Explanation:

• at: The command itself.
• -f path/to/file: Specifies the file that contains the commands to be executed.
• 9:30 PM Tue: Specifies the time of execution as 9:30 PM on the next Tuesday.

Example output:

warning: commands will be executed using /bin/sh
job 3 at Tue Jan 11 21:30:00 2022

In this example, the commands from the file specified by path/to/file will be executed at 9:30 PM on the next Tuesday and a job number (3) is assigned to it.

Conclusion:

The at command provides a convenient way to schedule the execution of commands at a later time. It can be used to automate tasks, delay command execution, or execute a sequence of commands stored in a file. By understanding the different use cases and the options available, you can effectively use the at command in your daily workflow.