How to Use the at Command in Bash for Scheduling Tasks

Use the at command in bash to schedule a command or script to run once at a specified future time. You type at [time], enter the commands, then press Ctrl+D to save and schedule the job.

Syntax

The basic syntax of the at command is:

• at [time]: Schedule commands to run at the specified time.
• After running this, you enter the commands you want to run later.
• Press Ctrl+D to finish and save the job.

bash

at 14:30
# type commands here
# press Ctrl+D to save

Example

This example schedules a message to be printed at 1 minute from now. It shows how to enter the command and the output of listing scheduled jobs.

bash

echo "echo 'Hello from at command!'" | at now + 1 minute
atq
# Wait 1 minute to see the message printed in the terminal or check the output file if redirected

Output

1	Thu Jun  1 14:31:00 2024 a user

Common Pitfalls

• Not pressing Ctrl+D after typing commands will not save the job.
• Using incorrect time formats can cause errors; use formats like HH:MM, now + 5 minutes, or tomorrow.
• at jobs run with your user permissions, so environment variables or paths may differ.
• Some systems may require atd service to be running for at to work.

bash

echo "date" | at 25:00
# Wrong time format, will cause error

# Correct way:
echo "date" | at 23:00

Quick Reference

Command	Description
at [time]	Schedule commands to run once at the specified time
atq	List pending at jobs
atrm [job_number]	Remove a scheduled at job
Ctrl+D	End input and save the at job

Key Takeaways

Use at [time] to schedule one-time commands in bash.

Type your commands after running at and press Ctrl+D to save.

Check scheduled jobs with atq and remove them with atrm.

Ensure the atd service is running for at to work properly.

Use correct time formats like HH:MM, now + 5 minutes, or tomorrow.