How to find day difference between a date with `YYYY-MM-DD` format and today's date in Unix shell script?

Question

I have a date say 2015-12-30. I want to find the day difference between this day and today's date.

Currently I am doing this

dest_date="2015-12-30"
now=`date +%Y-%m-%d`

echo "( `date -d $dest_date +%s` - `date -d $now +%s`) / (24*3600)" | bc -l

But this is giving error as

date: invalid date `+%s'
(standard_in) 1: parse error

Answer 1

You can simplify this:

dest_date="2015-12-30"
diff=$(( ($(date '+%s' -d "$dest_date") - $(date '+%s')) / 86400 ))

echo $diff
14