How do I convert a date string in format MMDDYYYY to YYYY-MM-DD at the Unix command line?

Question

From the Unix command line, how do I convert a date string in the format MMDDYYYY to the format YYYY-MM-DD? For instance, how do I convert 02032017 to 2017-02-03? Thanks!

I have tried this, but I'm afraid it did not work.

date -d "02032017"

This produces this error message.

date: invalid date ‘02032017’

Answer 1

String manipulation with variable expansions

input_date=02032017
output_date=${input_date:4}-${input_date::2}-${input_date:2:2}

Answer 2

This should work,

DATE="02032017"; date -d"$DATE" +%Y-%m-%d

Error in the above answer.

Try this one

month=$(cut -c 1-2)
date=$(cut -c 3-4)
year=$(cut -c 5-8)
date=$year-$month-$date
echo $date

Answer 3

You can use a date library that allows you to specify the incoming date's format, for example perl's Time::Piece :

input_date=02032017
perl -MTime::Piece -sE 'say Time::Piece->strptime($date, "%m%d%Y")->ymd' -- -date="$input_date"

2017-02-03

Answer 4

This should also work

date="02032017"
year=${date:4:4}
month=${date:0:2}
day=${date:2:2}
formatted_date=$year-$month-$day
echo $formatted_date