Linux date usage

Useful date functions

In bash script, date is really useful function. Below are some frequently used situations:

1. generate today's datetime:
In terminal:~$ date +%Y-%m-%dT%T
result: 2013-05-15T16:17:35
In bin/bash: date +"%Y-%m-%d %T"
result: 2013-05-15 16:17:35
NOTE: the usage of space. In the terminal, space or "" is not allowed.

2.generate date/datatime n days before:
In terminal: ~$date +%Y%m%d -d "60 days ago"  or  ~$date +%Y%m%d -d "60 day ago"
result: 20130316
In bin/bash: date +%Y%m%d -d "187 days ago" (same as terminal)

3. generate date in cron job

* * * * * test.sh `date +\%Y\%m\%d -d "1 days ago"`

4. Use variable in date
enddate=YYYYmmdd
test_date=$(date -d"${enddate} - 1 day" +%Y-%m-%d)
note: even need the same format as $enddate, the format definition in the red part still needs to be given.