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I have come across this weird behaviour of GNU date.

date -d "29-May-20 09:29 1 minute" +"%d-%b-%y %H:%M" 

gives output: 29-May-20 09:30 --> Note: I have given here the abbreviated month name format specifier '%b'

But,

date -d "29-05-20 09:29 1 minute" +"%d-%m-%y %H:%M"

gives output: 20-05-29 09:30 --> I mean the year and the date field is jumbled, though I have given the correct format specifier '%m' for the month field. How to make it work to give the expected output 29-05-20?

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    Read carefully about how GNU date parses user input: gnu.org/software/coreutils/manual/html_node/… => "For numeric months, the ISO 8601 format ‘year-month-day’ is allowed, where year is any positive number, month is a number between 01 and 12, and day is a number between 01 and 31. " Jan 21, 2021 at 20:09

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The +FORMAT describes the output, not how the argument to -d is parsed. If you want to ensure that is parsed the way you want, you should feed it an unambiguous representation

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  • Fox then it should be dd-mm-yy right? according to the format specifier "%d-%m-%y" but I am getting the yy-mm-dd as output Jan 21, 2021 at 9:07
  • not at all. let me rephrase: the format specifier has absolutely nothing to do with that argument. The fully-numeric date you've given is assumed to by yy-mm-dd (if possible), and is then output according to the format specifier, which has the dd part and the yy part in the opposite order
    – Fox
    Jan 21, 2021 at 15:44

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