Steps to create a permanent Bash alias:

Open the Terminal app

1. Edit ~/.bash_aliases or ~/.bashrc file using: vi ~/.bash_aliases
2. Append your bash alias
3. For example append: alias update='sudo yum update'
4. Save and close the file.
5. Activate alias by typing: source ~/.bash_aliases

Please note that ~/.bash_aliases file only works if the following line presents in the ~/.bashrc file:

if [ -f ~/.bash_aliases ]; then
. ~/.bash_aliases
fi

Are above lines are missing in your ~/.bashrc file? Just append at the end of the ~/.bashrc, using a text editor such as vi/vim or joe.

Examples

Let us create four aliases as follows:
$ vi ~/.bash_aliases
OR
$ joe ~/.bashrc
Append text:

# update our debian/ubuntu box
alias update='sudo -- sh -c "apt update && apt upgrade"'
 
# make grep output colorful 
alias grep='grep --color=auto'
 
# set eth0 as an interface for eth0  
alias vnstat='vnstat -i eth0'
 
# flush redis cache for wp
alias flush_redis='redis-cli -h 127.0.0.1 FLUSHDB'

Save and close the file.

How to load aliases

All new aliases will be available next time you login using a new ssh/terminal session. To load changes immediately, type the following source command:
$ source ~/.bash_aliases
OR
$ . ~/.bash_aliases

How to list all of my aliases

To list all aliases, run:
$ alias
Sample outputs:

alias flush_redis='redis-cli -h 127.0.0.1 FLUSHDB'
alias grep='grep --color=auto'
alias l='ls -CF'
alias la='ls -A'
alias ll='ls -alF'
alias ls='ls --color=auto'
alias update='sudo -- sh -c "apt update && apt upgrade"'
alias vnstat='vnstat -i eth0'

How to use/call aliases

Just type alias name:
$ update
$ vnstat
$ flush_redis

Summary of all commands

See also 30 Handy Bash Shell Aliases For Linux / Unix / Mac OS X and bash command man page here.