How to change the root password via a shell script or command line?

Which can be use which it!

method one,

echo -e "newpwd\nnewpwd" | (passwd root)

 

Method Two,

echo "newpwd" | passwd root --stdin > /dev/null 2>&1

 

Method three,

# If the password is included in $ characters, use a backslash (\) escape
echo root: newpwd123 \ $ | chpasswd

Openwrt | openwrt compile time, how to specify the root password
CAT / etc / Shadow
root: $ 1 $ HSk7yPlb $ 6cPCTE8gYv2AxBvGdwCgS /: 17949: 0: 99999: 7 :::

package/base-files/files/etc/shadow

Reference:
https://stackoverflow.com/questions/714915/using-the-passwd-command-from-within-a-shell-script