Ubuntu has bower and gulp installed, but cannot run?

  node.js, question
weharvest@weharvest:~$ sudo npm install bower -g
 /opt/node-v6.6.0-linux-x64/bin/bower -> /opt/node-v6.6.0-linux-x64/lib/node_modules/bower/bin/bower
 └── bower@1.7.9
 weharvest@weharvest:~$ bower install
 The' bower' command was not found. Do you want to enter:
 Command' boxer' comes from package' boxer' (universe)
 Bower: command not found

Nodejs -v or npm -v can be used.
Help! ! !

Later, it was found that adding/opt/node-v6.6.0-Linux-x64/lib/node _ modules/bow/bin to the environment variable was enough.
But every time you install one, you have to add one manually. Is there any way to make it automatic?

Bower can, but gulp can’t. . . . .

Add /opt/node-v6.6.0-linux-x64/bin to environment variable