How to restore the computer's username in Terminal? I would like to restore the previous name (default) in my terminal. How can I do that? 

I changed to $ sign only by applying this code:

echo "export PS1='$ '" &gt;&gt; ~/.bash_profile
. ~/.bash_profile


but couldn't manage to restore it.
Simply enter

nano ~/.bash_profile


then go to the line

export PS1='$ '


and delete that line. Then save the file and exit nano. After then execute

. ~/.bash_profile


That will be load the settings from this file.