Compatible with macOS Big Sur 11 and later.

IMPORTANT: Until I have the opportunity to fix it, please note that changes in macOS Monterey 12.4 have temporarily broken this script.

Set the date and time format of the menu bar clock from the command line in macOS Big Sur 11 and later.

Please note, the script simply mimics what can otherwise be achieved by setting the format through System Settings¹ System Preferences. It is therefore limited to the formats defined by Apple.

1. Download menu-bar-clock-main.zip

2. Double-click ~/Downloads/menu-bar-clock-main.zip in the Finder to unzip it (Safari may do this automatically)

3. Open the Terminal application in macOS

4. At a Terminal prompt:

   1. type cd ~/Downloads/menu-bar-clock-main and press enter

   2. type chmod +x menu-bar-clock.sh and press enter to make the script executable

   3. use one of the commands under the Command Line heading in the table below to set the required date and time format

Starting with macOS Monterey 12.4, Apple have made changes to the Show date option in System Settings > Desktop & Dock > Clock Options...² System Preferences > Dock & Menu Bar > Clock. Previously, it was either checked or unchecked and set the value of the ShowDayOfMonth key in the com.apple.menuextra.clock domain to either true or false respectively. This key now appears redundant. Instead, the Show date option offers 3 new choices which are written to a new key in the com.apple.menuextra.clock domain named ShowDate.

To support the changes to the Show date option in macOS Monterey 12.4, the script accepts a new option: -s. The option need only be passed to the script when the desired date format contains d MMM i.e. 18 Aug and you want that date portion displayed when space allows. In all other circumstances it can be omitted, as per the table below. If the option is passed to the script it will be ignored when the date format doesn't contain d MMM or the installed macOS version is macOS Monterey 12.3.1 or earlier or macOS Big Sur 11.

The Menu Bar Clock values in the table above are localised and based on a Region setting of United Kingdom in System Settings > General > Language & Region² System Preferences > Language & Region > General. Other Regions may display the same date and time format differently. For example, the format "EEE d MMM HH:mm" is displayed differently for the following Region settings:

In addition, the primary preferred language setting also in System Settings > General > Language & Region² System Preferences > Language & Region > General may affect how the date and time is displayed.

Prior to macOS Big Sur 11, setting the date and time format of the menu bar clock from the command line was relatively trivial.

Challenges to setting the date and time format of the menu bar clock introduced in macOS Big Sur 11 include:

• Additional keys in the com.apple.menuextra.clock domain.

• A (re-purposed?) 24-Hour Time option in System Settings¹ System Preferences which overrides time settings.

• The SystemUIServer process no longer appears responsible for displaying the date and time in the menu bar.

In macOS Big Sur 11 and later, the structure of com.apple.menuextra.clock.plist has changed:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>DateFormat</key>
	<string>EEE d MMM HH:mm</string>
	<key>FlashDateSeparators</key>
	<false/>
	<key>IsAnalog</key>
	<false/>
	<key>Show24Hour</key>
	<true/>
	<key>ShowAMPM</key>
	<false/>
	<key>ShowDate</key>         <--- New key as of macOS Monterey 12.4
	<integer>0</integer>
	<key>ShowDayOfMonth</key>   <--- Appears redundant as of macOS Monterey 12.4
	<true/>
	<key>ShowDayOfWeek</key>
	<true/>
	<key>ShowSeconds</key>
	<false/>
</dict>
</plist>

The additional keys are Show24Hour, ShowAMPM, ShowDate ³, ShowDayOfMonth³, ShowDayOfWeek and ShowSeconds.

Prior to macOS Big Sur 11, only the DateFormat key need be set using a single defaults write command. Now, multiple defaults write commands are required to set the DateFormat key together with the 5 additional keys.

This option can be found in System Settings > General > Date & Time² System Preferences > Language & Region > General and may override the keys Show24Hour and ShowAMPM depending on their values. It is also used to format the display of dates and times in the Finder. This option exists in Catalina too, but doesn't appear to assert the same control as it does in macOS Big Sur 11 and later.

While this option can be turned on checked or off unchecked from within System Settings¹ System Preferences, it can be toggled from the command line using the AppleICUForce12HourTime key in the .GlobalPreferences domain.

When the option is off unchecked, the AppleICUForce12HourTime key has a boolean value of true. When on checked, the key is deleted from the .GlobalPreferences domain.

Any attempt to set the date and time format from the command line should ensure that this key exists or not based on the values of the Show24Hour and ShowAMPM keys, or vice versa.

Prior to macOS Big Sur 11, restarting the SystemUIServer process updated the date and time format of the menu bar clock with any changes to the DateFormat key.

This is no longer true in macOS Big Sur 11 and later. The process that controls the menu bar clock is ControlCenter which needs to be restarted (killed) after changes have been made to the com.apple.menuextra.clock and .GlobalPreferences domains.