Looking for Shell Script to compare the file size?

Hi Guys,

Hope you all doing good,

Am looking for shell script to compare the file size of yesterday file & todays file the filename along with date for example backup-12-06-2016

yesterday file will be - backup-12-06-2016
today file will be - backup-13-06-2106

I want to compare both file and if the file size is lesser than yesterday’s file means need to send a email to admin@example.com

can anyone help me out this thanks in advance

I have tried below, but achieved