Search notes:

net localgroup

net localgroup is a command line (cmd.exe) tool used to administer a local group on a computer. In contrast, to modify global groups in domains, net group is used.

Show members of the (local) Administrators group

net localgroup Administrators
This command shows the members of the (local) Administrators group. If I am listed in them, I have administrator permissions on the machine.
In order to check in what groups I am, I can use whoami /groups.

Adding a user to the Administrators group

The following command adds user Rene to the Administrators group: 
net localgroup Administrators Rene /add

See also

net.exe

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