MacOS – How to persistently define aliases in Terminal

All you need to do is type alias at the prompt and any active aliases will be listed.

Aliases are usually loaded at initialization of your shell so look in .bash_profile or .bashrc in your home directory.

unalias will only work for your current session. Unless you find where it is defined and loaded, it will be loaded again when you start a new Terminal session.

~/.bashrc gets run for both login and non-login shells, ~/.bash_profile only gets run for login shells.

See login shell vs non-login shell

As per comment from Chris Page:

You should put most of your customizations (including aliases) in ~/.bashrc and have ~/.bash_profile run ~/.bashrc, so they apply to both login (~/.bash_profile) and non-login (~/.bashrc) shells. Also, decide which of these should be "primary" and if the profile is your choice, tack on the rc file at the end. If the rc file is primary, source that at the beginning of your profile

These lines should be in the file ~/.bash_profile:

if [ -f "$HOME/.bashrc" ] ; then
  source $HOME/.bashrc
fi

This will include ~/.bashrc for login shells and in the order you wish if one file depends upon the other based on what you are setting.

The problem you are encountering is that when you run su by itself, you are not entering a 'login' shell. This means that your environment, working directory, and everything except uid/gid remain the same of the original user.

Login triggers do not execute, and you experience the issues you describe.

A simple solution to a simple problem:

su -

From the su(1) man page:

The su command is used to become another user during a login session. Invoked without a username, su defaults to becoming the superuser. The optional argument - may be used to provide an environment similar to what the user would expect had the user logged in directly.

Also:

   -, -l, --login
       Provide an environment similar to what the user would expect had the user logged in directly.

If you su into a login shell, bash will behave as you expect, and automatically source the appropriate files on "login", without the need for overly hacky workarounds.