How to update PATH variable permanently from Windows command line?

You can use:

setx PATH "%PATH%;C:\\Something\\bin"

However, setx will truncate the stored string to 1024 bytes, potentially corrupting the PATH.

/M will change the PATH in HKEY_LOCAL_MACHINE instead of HKEY_CURRENT_USER. In other words, a system variable, instead of the user’s. For example:

SETX /M PATH "%PATH%;C:\your path with spaces"

You have to keep in mind, the new PATH is not visible in your current cmd.exe.

But if you look in the registry or on a new cmd.exe with "set p" you can see the new value.