Looking for a linux tool to automate PG admin tasks

Hello,
I have several servers with many databases on them for different 
applications.
I need to execute some tasks on some databases depending on some criteria.

For example, execute query xxx but only on databases where table 
public.sometable exists or if number of rows in table yyy is > 1M.
Before reinventing the wheel with ugly bash scripts, do you know of some 
tools that would suit my case ?
Some tasks will have to execute periodically (with crons probably) and 
others will be one-off.
CLI tools if possible because I'm working remotely on those servers of 
course.
Thanks,
JC