UNIX for Dummies Questions & Answers

#!/bin/bash

# figure out what yesterday was.
date '+%Y %m %d' |
 {
 read year month day

 day=`expr "$day" - 1`
 case "$day" in
 0)
 month=`expr "$month" - 1`
 case "$month" in
 0)
 month=12
 year=`expr "$year" - 1`
 ;;
 esac

 day=`cal $month $year | grep . | fmt -1 | tail -1`
 esac

 echo "Yeseterday was: $day $month $year"
                 }

date --date=yesterday

print scalar localtime (time() - 86400 * n);

print scalar localtime (time() - 86400 * 1); #yesterday
print scalar localtime (time() - 86400 * 30); #Date of 30 days back

print scalar localtime (time() + 86400 * 4);