BASH / Linux-从变量中查找下一个日期

Question

In my Unix shell programming, I am trying to get the next date (tomorrow's date) over a reference date defined as "a". Here is the code:

a=2016-01-02

Which operator would I use in my code so that Unix will automatically define a as tomorrow's date as in below

a=2016-01-03

Answer 1

date has a -d option that is very useful in this situation.

To get the next day, add a space after the date then add 1 day

date +%Y-%m-%d -d "$a 1 day"

It's important to add the format specifier because without it, you would get the following output

=>"Sun Jan 3 00:00:00  UTC 2016"

To update the a variable, you could do something like this

a=$(date +%Y-%m-%d -d "$a 1 day")

Remember to wrap the command inside of parentheses with a $ sign in front of it.