Why is my variable available through echo, but not through printenv?

Question

When first installing powerlevel10k, one usually follows the guides available on the Internet and clone the repository inside oh-my-zsh's folder:

git clone --depth=1 https://github.com/romkatv/powerlevel10k.git ${ZSH_CUSTOM:-$HOME/.oh-my-zsh/custom}/themes/powerlevel10k

Now, if I echo $ZSH_CUSTOM I will get /home/myuser/.oh-my-zsh/custom as expected, but printenv will not list it at all. Why is that?

Does this answer your question? Is `env` not to print out the environment in the current shell, but the environment received within `env`? — muru, May 10 '21 at 14:45

score 3 · Accepted Answer · answered May 10 '21 at 23:47

The :- in the variable tells bash (or zsh) to use whatever is after the - as the default value. If ZSH_CUSTOM is not in your environment variables (it doesn't show up in printenv), it will default to $HOME/.oh-my-zsh/custom.

You can try it yourself:

echo ${MY_VARIABLE}
# prints an empty line
echo ${MY_VARIABLE:-a default value}
# prints: a default value

Why is my variable available through echo, but not through printenv?

1 Answers1