Using date command to get previous current and next month

Question

I am using below to get previous  current and the next month under Ubuntu 11 04   LAST MONTH  date    m  -d  last month   NEXT MONTH  date    m  -d  next month   THIS MONTH  date    m  -d  now     It works well until today  the last day of October  2012  2012-10-31   I get below result as of now     date Wed Oct 31 15 35 26 PDT 2012   date    m  -d  last month  10   date    m  -d  now  10     date    m  -d  next month  12   I suppose the outputs should be 9 10 11 respectively   Don t understand why date outputs behave like this  What should be a good way to get consistant previous  current and next month instead

User · Accepted Answer

The problem is that date takes your request quite literally and tries to use a date of 31st September  being 31st October minus one month  and then because that doesn t exist it moves to the next day which does  The date documentation  from info date  has the following advice      The fuzz in units can cause problems with relative items   For   example   2003-07-31 -1 month  might evaluate to 2003-07-01  because   2003-06-31 is an invalid date   To determine the previous month more   reliably  you can ask for the month before the 15th of the current   month   For example      date -R  Thu  31 Jul 2003 13 02 39 -0700    date --date  -1 month    Last month was  B    Last month was July     date --date    date   Y- m-15  -1 month    Last month was  B    Last month was June

User · Answer

the following will do   date -d    date   Y- m-1  -1 month    -m date -d    date   Y- m-1  0 month    -m date -d    date   Y- m-1  1 month    -m   or as you need   LAST MONTH  date -d    date   Y- m-1  -1 month    -m  NEXT MONTH  date -d    date   Y- m-1  1 month    -m  THIS MONTH  date -d    date   Y- m-1  0 month    -m    you asked for output like 9 10 11  so I used the  -m   m  without -  will produce output like 09      leading zero   this also works for more less than 12 months   date -d    date   Y- m-1  -13 month    -m   just try  date -d    date   Y- m-1  -13 month    to see full result

User · Answer

the main problem occur when you don t have date --date option available and you don t have permission to install it  then try below -   Previous month  cal -3 awk  NR  1 print toupper substr  1 1 3   -  2   DEC-2016  Current month  cal -3 awk  NR  1 print toupper substr  3 1 3   -  4   JAN-2017 Next month  cal -3 awk  NR  1 print toupper substr  5 1 3   -  6   FEB-2017

User · Answer

If you happen to be using date in a MacOS environment  try this   ST1   ejf  date Mon Feb 20 21 55 48 CST 2017 ST1   ejf  date -v-1m   m 01 ST1   ejf  date -v 1m   m 03   Also  I d rather calculate the previous and next month on the first day of each month  this way you won t have issues with months ending the 30 31 or 28 29  Feb Feb leap year

[linux] Using `date` command to get previous, current and next month

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