I had a similar problem setting it up in windows 10. My answer is windows specific (look at the answers for modifying path in bash for a linux or OSX solution)
The core problem I had was that npm's folder was not registered in the path.
I originally tried changing this in cmd prompt.
setx path "%path%;%appdata$\npm"
Note that I used setx instead of set to ensure that the update to the environmental variable remains. Also note that it's a backslash.
This should work but for me it didn't because setx has a limit of only accepting 1024 characters... (yes it's nonsensical to me as well).
So try the above and if you get a warning like did about reaching the 1024 limit, then you can do the other way I ended up doing.
First while youre still in the console, type: echo %appdata%\npm
... this is your npm folder that you want to add to the path so add it to your clipboard.
You have to go into the registry and reach the following folder:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Environment
Then append the 'Path' value with the npm folder path in your clipboard. Reboot to activate the new value and you should now be good to go.
Finally, just test it all out
>npm install -g gulp
>gulp
npm install gulp --save-dev
? – soenguygulp
program lies to the Windows %PATH% variable. In my case:%AppData%\Roaming\npm
– AdrienW