[SOLVED] How to sort DD-MM-YYYY dates linux

Issue

I have dates in a DD/MM/YYYY format, with the caveat that for days <10 dates are single digits.

Some example data is below:

name,date,time
DEF,1/02/2021,06:00
HIJ,31/01/2021,07:50
ABC,1/04/2021,05:50

I only want to sort by the date column. I find this challenging since the days part of the date value is variable in length.

Solution

There isn't an easy way to sort the date field ([d]d/mm/yyyy) directly within a comma-separated field (sort natively understands US mm/dd/yyyy style dates but not this international alternative). However, picking out that date field and reordering the fields as yyyy-mm-dd makes it much easier, and sort can handle this as a standard alphanumeric sort. The process of temporarily pulling out the primary sort key is known as a Schwartzian transform.

Here you would sort the result, then throw away this first (temporary) field to regain the original unchanged data.

awk -F'[,/]' '{printf "%04d-%02d-%02d\t%s\n", $4,$3,$2, $0}' datafile | sort | cut -f2-

name,date,time
HIJ,31/01/2021,07:50
ABC,1/02/2021,05:50
DEF,1/02/2021,06:00

You can see the result of the intermediate process if you strip back either before or after the sort command.

Answered By - roaima

Answer Checked By - Gilberto Lyons (WPSolving Admin)