! is a valid character in an alias. I use it to mark aliases which run under sudo, for example on my Debian box I have:
alias e!=”sudo ${EDITOR}”
alias a!=”sudo apt”
alias s!=”sudo systemctl”
alias in!=”sudo apt install”
alias a!=”sudo apt”
alias s!=”sudo systemctl”
alias in!=”sudo apt install”
… and a few others.
