Get today's date minus one Year in Unix (AIX) - shell

Question

I need to find today's date and then subtract a year and format that date into the YYYY-MM-dd format.
I am able to accomplish this with a script I wrote, but apparently it is only compatible with bash. I need it to be compatible with AIX.
lastYear=`date +'%Y-%m-%d' -d 'last year'`
searchDate="$lastYear 00.00.00";
echo "Retrieving data start from $searchDate"
myquery="myquery >= '$searchDate'"
The result when run on an AIX machine is that it only passes the "00:00:00" part of the $searchDate, the date does not prefix before the time as I hoped. What is the safest way to write this for the most compatibility across Linux/Unix variations?
Thank you!

Answer 1

Why make it so complicated?
#!/bin/ksh
typeset -i year=$( date +%Y )
(( year -= 1 ))
typeset rest=$( date +%m-%d )
echo "${year}-${rest}"
This should work in any shell. If you use sh replace the
$( ... )
with back tics
` ... `
But for bash and ksh I use $( ... ) -- just personal preference.

Answer 2

Checkout Updated Section Below
Original Answer
Try this. It uses the -v flag to display the result of adjusting the current date by negative one year -1y
searchDate=$(date -v-1y +'%Y-%m-%d')
echo "Retrieving data start from $searchDate"
myquery="myquery >= '$searchDate'"
Here is the output:
Retrieving data start from 2017-06-21
Note: I did try to run the lines you provided above in a script file with a bash shebang, but ran into an illegal time format error and the output was 00:00:00. The script I provided above runs cleanly on my unix system.
Hope this helps. Good luck!
Updated Section
Visit ShellCheck.net
It's a nice resource for testing code compatibility between sh, bash, dash, and ksh(AIX's default) shells.
Identifying the Actual Issue
When I entered your code, it clearly identified syntax that is considered legacy and suggested how to fix it, and gave this link with an example and a great explanation. Here's the output:
lastYear=`date +'%Y-%m-%d' -d 'last year'`
^__Use $(..) instead of legacy `..`.
So, it looks like you might be able to use the code you wrote, by making one small change:
lastYear=$(date +'%Y-%m-%d' -d 'last year')
Note: This question already has an accepted answer, but I wanted to share this resource, because it may help others trouble-shoot shell compatibility issues like this in the future.