How can I determine the battery level of my magic mouse from the command line?

I know how to get it through the menubar, but how can I get it via the command line?

Use ioreg and search for battery using grep

• Check the battery level of connected bluetooth headphones from the command line?

Since ioreg is really verbose - here is one command that cuts down to the names of bluetooth devices and all percentage of battery for each.

ioreg -l |egrep "BatteryPercent|Bluetooth Product Name"

Building on useful answer from bmike [Jul 30 '17] ... with a way to further cut down the repetitions of device names: add (a) symbol carat (^) to signify start-of-line, and (b) escaped vertical bar preceded and followed by specific number of spaces:

 ioreg -r -l -n AppleHSBluetoothDevice | egrep '"BatteryPercent" = |^  \|   "Bluetooth Product Name" = '

Those filters yielded this result:

     |   "Bluetooth Product Name" = "Magic Keyboard with Numeric Keypad"
     |   |       "BatteryPercent" = 59
     |   "Bluetooth Product Name" = "Magic Mouse 2"
     |   |       "BatteryPercent" = 98

More filtering with sed and echoing the variable gave the result that I was looking for

    BATTLVL=$(ioreg -r -l -n AppleHSBluetoothDevice | egrep '"BatteryPercent" = |^  \|   "Bluetooth Product Name" = '| sed 's/  |   "Bluetooth Product Name" = "Magic Mouse 2"/  \|  Mouse:/' | sed 's/  |   "Bluetooth Product Name" = "Magic Keyboard with Numeric Keypad"/  \|  Keyboard:/'| sed 's/  |   |       "BatteryPercent" = / /'); echo $BATTLVL 

The result in console:

     | Mouse: 96 | Keyboard: 71

But, when I went to put it all into a bash script file, I found that while BATTLVL indeed contains only the desired words and phrases to be reported, it also contains newline characters -- but, they do not appear when the ECHO command is appended to the preceding command with a semicolon.

So, in order to make further use of the report results, we remove the newlines using techniques suggested in this post:

    BATTRPT=${BATTLVL//[$'\t\r\n']};  # Strips all instances of tab, newline, return.

Finally, to add an OS X notification of mouse and keyboard battery level from the bash script, found it necessary to first build the script string into a variable, and then pipe it to osascript so that the double quotes would be included in the string.

    theScript=$"display notification \"$BATTRPT\" "
    echo $theScript | osascript