But, I can't find proper event to run on save.
Theres simply no such hook, but you can override the GUI functions easily. You simply cant go around developping for maya and thinking events yeah tahts what i need.
You jout can't just expect override EVERYTHING anybody wishes to do in script, In fact even with a scriptjob with this hook you couldn't because the script can allways counterwork you. Its a questionn of priority last come last first served, ultimately users have the last word and theres NOTHING you can do about that no matter how much youd wish otherwise. See this kind of design is paradoxal, as the act of giving you something gives it to everybody else
I just want to backup the scene information before save the scene.
use version controll, seriously. Or in pinch use the builtin incremental save stuff in maya menus.
For example:
when a may users chooses save a mel runtime command is called, now maya IS mel* o. Suppose you want to get in between the file -> save Scene and the ctrl+s shortcut.
Youd go:
over to mayDirectory/Startup/FileMenu.mel and COPY (IMPORTANT!!) that file over to your personal or studio* mel script folder and change the global proc FileMenu_SaveItem
*dont have a studio wide folder? Well make one.