Oh boy. Lots of stuff there will break your script.

First, you need a way for the script to know what name you want. Besides that, the script would look more like this:

#!/bin/sh

scutil --set ComputerName $setName
scutil --set HostName $setName
scutil --set LocalHostName $setName

If you are trying to read in the ComputerName and set that for the other two names, that would look like:

#!/bin/sh

setName=$(scutil --get ComputerName)
scutil --set HostName $setName
scutil --set LocalHostName $setName

This is what mines looks like:

!/bin/bash

Simple script that names the computer.

Last 8 characters of the Serial Number:

definedComputerName="/usr/sbin/system_profiler SPHardwareDataType | awk '/Serial Number/ { print $NF }' | rev | cut -c 1-8 | rev"

/usr/sbin/scutil --set ComputerName ${definedComputerName}
/usr/sbin/scutil --set LocalHostName ${definedComputerName}
/usr/sbin/scutil --set HostName ${definedComputerName}

exit 0

If you are talking about Jamf managed Macs, you could also use the Jamf binary to accomplish this with less hassle:

computerName="populate_this_however_you_want"
jamf setComputerName -name "$computerName"