adding PATH with SETX or PATHMAN or something else?

See the article Edit the PATH environment variable in Windows without pain.

It recommends using pathed :

For example, say that you have your Sysinternal tools in C:\Bin\Sysinternals and you want to add them to the PATH. Simply do:

pathed /append C:\Bin\Sysinternals /machine

If you want to add them to the user PATH system instead, then do:

pathed /append C:\Bin\Sysinternals /user

(I know that you've already answered this question, but)

The problem with your usage of setx is that you are not quoting the string that you want to be set. Because the ; character is a command delimiter (you can string commands to be run in-succession with it), it thinks that you are setting path and then running another command.

What you should do is this:

setx /M path "C:\perl\bin;%path%"

This prepends my %path% variable with C:\perl\bin, because I want it to come before anything else that may be installed. The /M means that I mean the System EnvVar, not the user's.