Explain this command: . ~/nvm/nvm.sh

Question

I am by no means a novice user on Linux, but I just don't understand why one has to put . in front of this command:

. ~/nvm/nvm.sh

For those in the know, this is how to activate the nvm bash script (it allows for a virtual environment in the NodeJS universe). But if one does not put that starting period in front of the command, then things don't work out. As far as I know, the "." means current directory. Yet if I do this:

cd ~/nvm
nvm.sh

or this

~/nvm/nvm.sh

It will not work. Why? Why must one put "." and then a space before running this command.

Answer 1

. ~/nvm/nvm.sh

It asks the interpreter to interpret the script in the current process. In bash it's equivalent to:

source ~/nvm/nvm.sh

You need to execute a script in the current process if you want it to change the environment (variables, et al). You can view more details with help .

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~/nvm/nvm.sh

This one actually runs the script in a new bash process. It cannot change the environment of the parent, for example it cannot export variables to the parent process.

Answer 2

The . means run in the current shell so environment variables you've set or are set in the script are shared. I would wager launching a new shell for the script puts it in an environment it cannot run in.