BASH Shell - untuk mencari tanggal kemarin

isguo@localhost $ date +%Y-%m-%d -d "1 day ago"
2011-12-20
:~
isguo@localhost $ date +%Y-%m-%d -d "1 day ago"
2011-12-20
:~
isguo@localhost $ date +%Y-%m-%d -d "1 week ago"
2011-12-14
:~
isguo@localhost $ date +%Y-%m-%d -d "1 month ago"
2011-11-21