Get the date of last month's last day in a shell script

Question

How do I get the previous month end date, based on processing date?

Examples:

• Processing date = 15jan2015
• Expected date = 31dec2014,

---

• Processing date = 10feb2015
• Expected date = 31jan2015

Answer 1

With GNU date:

$ date +%d%b%Y
16Aug2015
$ date -d "$(date +%Y-%m-01) -1 day" +%d%b%Y
31Jul2015

Some shells have built-in support for date manipulation:

With ksh93:

$ printf "%(%d%b%Y)T\n" "1st day, yesterday"
31Jul2015

With zsh:

$ zmodload zsh/datetime
$ strftime -s d %Y-%m-01-12 $EPOCHSECONDS
$ strftime -rs d %Y-%m-%d-%H $d
$ strftime %d%b%Y $((d-86400))
31Jul2015

Answer 2

Here's a version that works on Mac OS, which uses the BSD date utility:

date -v1d -v-1d +%d%b%Y

The arguments are applied in order. You can kind of imagine that a date is piped from one argument to the next. For example:

• Start with the current date (date) -> 2017-03-06
• Set that date to the 1st day of its month (-v1d) -> 2017-03-01
• Subtract one day from that (-v-1d) -> 2017-02-28
• Format the date (+%d%b%Y) -> 28Feb2017

You can reach any number of months forward or backward using date -v-1m -v1d -v-1d, replacing -1m with the number of months backwards or forwards (+1m) you want.

That's the generic answer. This question specifically asks about dates relative to a starting date. The Mac OS / BSD date utility doesn't let you supply a datestamp to start from, but you can set each date element individually:

date -v2015y -v1m -v15d -v1d -v-1d +%d%b%Y -> 31Dec2014

Answer 3

There are a lot of ways to do this; here is the simplest one I found (here assuming GNU date):

$ date -d "-$(date +%d) days"
Fri Jul 31 16:07:23 EDT 2015

Answer 4

Try using this code

date -d "-$(date +%d) days  month" +%Y-%m-%d