How do I get the month one calendar month ago in bash?

Question

I have been using the command:

date --date='1 months ago' +%b

To get the month name of the month it was a month ago, but have realised today as it is the 31st that this command actually gives me the month name it was 4 weeks ago.

Is there any way to get the calendar month that it was 1 month ago, or indeed n months ago as I can see that the discrepancy will be greater as the number of months is longer.

You can find the answer here : http://stackoverflow.com/questions/13168463/using-date-command-to-get-previous-current-and-next-month — Arno, Jul 31 '14 at 15:29
It's because there's no 31st June. This is explained well in the duplicate question. — Tom Fenech, Jul 31 '14 at 15:33

score 1 · Answer 1 · answered Jul 31 '14 at 15:31

Date calculations that depend on the number of days in the month are tricky. A hybrid approach, using month numbers and a lookup table, will probably work best.

months=("" Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec)
echo ${months[$(date +%m) - 1 ]}

score 0 · Answer 2 · answered Jul 31 '14 at 15:34

0

[[ $(date +%d) == "31" ]] && date -d'-31 day' +%b || date -d'-1 month' +%b

test with today:

kent$ date
Thu Jul 31 17:34:27 CEST 2014

kent$ [[ $(date +%d) == "31" ]] && date -d'-31 day' +%b || date -d'-1 month' +%b
Jun

answered Jul 31 '14 at 15:34

Kent

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score 0 · Answer 3 · answered Jul 31 '14 at 15:35

0

try this one line

#if the month before 30 days is the same of the actual month ,then return the month before 31 days

[[ `date --date='30 day ago' +%b` == `date +%b` ]] && echo `date --date='31 day ago' +%b` || echo `date --date='30 day ago' +%b`

answered Jul 31 '14 at 15:35

bachN

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How do I get the month one calendar month ago in bash?

3 Answers3