at:tldr:87c5c

This command is used to schedule a notification to be displayed on the screen at a specified time. Let me break it down:

• echo is a command that simply outputs whatever is passed to it.
• "notify-send '${Wake up!}'" is a string enclosed in double quotes. It consists of the notify-send command followed by the notification message 'Wake up!'. The message is enclosed within single quotes to preserve the exclamation mark within the string.
• | is a pipe symbol used to redirect the output of the preceding command to the input of the next command.
• at is a command used to schedule other commands or scripts to be executed at a specific time.
• ${11pm} specifies the time at which the notification should be displayed. The format used here is 11pm, indicating 11 o'clock in the evening.
• ${Feb 18} sets the date for the scheduled notification. It uses the format Feb 18, indicating February 18th.

In summary, this command schedules a notification using the notify-send command to be displayed on the screen at 11 pm on February 18th with the message "Wake up!"