This script checks for if the Mac is an M1 Chip, then if it is not, will check for the OS. Depending on these conditions, the year will be read differently.

#!/bin/sh #Set variables for processor, apple chip, & operating system version

processor=$(/usr/sbin/sysctl -n machdep.cpu.brand_string )
AppleChip="Apple M1"
AppleChipYear=$(/usr/libexec/PlistBuddy -c "print :'CPU Names'" ~/Library/Preferences/com.apple.SystemProfiler.plist | tr ' ' ' ' | grep -e "M1, 20[0-9][0-9]" -e "20[0-9][0-9]" | sed 's/[[:punct:]]$//' )
os_ver=$(sw_vers -productVersion | awk -F. '{print $2}')
os_ver2=$(sw_vers -productVersion | awk -F. '{print $1}')

#check if the machine is an Apple M1 processor

if [[ "$processor" == *"$AppleChip"* ]]; then
echo "$AppleChipYear" else

#Check which operating system version is on the mac if not an Apple M1 chip processor

if [[ ${os_ver} -le 14 ]] && [[ ${os_ver2} -le 10 ]]; then plistFile="/System/Library/PrivateFrameworks/ServerInformation.framework/Versions/A/Resources/English.lproj/SIMachineAttributes.plist"
sysModel=$(sysctl hw.model | awk '{print $NF}')
modelYear=$(/usr/libexec/PlistBuddy -c "Print ${sysModel}:_LOCALIZABLE_:marketingModel" "$plistFile" | tr ' ' '\\n' | grep -o "20[0-9][0-9]") if [ ! -z "$modelYear" ]; then
echo "$modelYear"
else
echo "N/A"
fi
elif [[ ${os_ver} -ge 15 ]]; then plistFile="/System/Library/PrivateFrameworks/ServerInformation.framework/Versions/A/Resources/en.lproj/SIMachineAttributes.plist"
sysModel=$(sysctl hw.model | awk '{print $NF}') modelYear=$(/usr/libexec/PlistBuddy -c "Print ${sysModel}:_LOCALIZABLE_:marketingModel" "$plistFile" | tr ' ' '\\n' | grep -o "20[0-9][0-9]") if [ ! -z "$modelYear" ]; then
echo "$modelYear"
else
echo "N/A"
fi
elif [[ ${os_ver} -le 14 ]] && [[ ${os_ver2} -ge 11 ]]; then
plistFile="/System/Library/PrivateFrameworks/ServerInformation.framework/Versions/A/Resources/en.lproj/SIMachineAttributes.plist"
sysModel=$(sysctl hw.model | awk '{print $NF}')
modelYear=$(/usr/libexec/PlistBuddy -c "Print ${sysModel}:_LOCALIZABLE_:marketingModel" "$plistFile" | tr ' ' ' ' | grep -e "M1, 20[0-9][0-9]" -e "20[0-9][0-9]" | sed 's/[[:punct:]]$//')
if [ ! -z "$modelYear" ]; then
echo "$modelYear"
else
echo "N/A"
fi
fi
fi
#end
exit 0