tomorrow / yesterday
Yes, you have "date" command to know what is the date today. Then how about tomorrow?
Fortunately, GNU's date command can display any date what you want to know. I recommend you to create following aliases for your shell.
alias tomorrow='date -d1day'(sh)
alias tomorrow 'date -d1day'(csh)
And variations.
alias yesterday='date -d1day+ago'(sh)
alias yesterday 'date -d1day+ago'(csh)
alias dayafter='date -d2day'(sh)
alias dayafter 'date -d2day'(csh)
alias daybefore='date -d2day+ago'(sh)
alias daybefore 'date -d2day+ago'(csh)
Tips: GNU date command accepts following options.
date -dtomorrow
date -dyesterday