Get the date (a day before current time) in Bash

if you have GNU date and i understood you correctly

$ date +%Y:%m:%d -d "yesterday"
2009:11:09

$ date +%Y:%m:%d -d "1 day ago"
2009:11:09

If you have BSD (OSX) date you can do it like this:

date -j -v-1d
Wed Dec 14 15:34:14 CET 2011

Or if you want to do date calculations on an arbitrary date:

date -j -v-1d -f "%Y-%m-%d" "2011-09-01" "+%Y-%m-%d"
2011-08-31

date --date='-1 day'

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