Whenever I open the Mac Terminal it shows "no such files or directory"
Whenever you open terminal some scripts are automatically called.

Programs (and users) add different commands to those files to set up their environment.

In default OS X configuration you are running a Bash shell which might run the following scripts:


~/.bash_profile (most probable)
~/.bashrc
/etc/bashrc
other can also be included from the above


You need to check (display for example with command cat ~/.bash_profile) each of them and search for the string USERNAME that is in the error message.

The next step depends solely on the content of the file. You might remove the offending lines or (safer) comment them out (putting # in front of the line).