How to create a while-do loop in a script to check if the file is empty?

Question

zsh

This is my first time writing a script.
You need to create something like this: check the file until it turns out that it exists and is not empty (there will be a certificate in the file)

While [test shows that the file either does not exist or is empty]
Do
Check again if the file exists and is empty file
Done

Tried this, doesn't work:

IsFileEmptyOrMissing(){
file="$1"
[ ! -s "${file}" ] && return 0 || return 1
}

IsFileEmptyOrMissing "ca.crt" >res
Cat res (empty)
x=$(cat res)

while [ $x != 0 ]
Do
IsFileEmptyOrMissing "ca.crt" >res
x=$(cat res)
Done

The file "ca.crt" now definitely exists for the test, it lies in the folder along with the script.

Answer 1

check the file until it appears that it exists and is not empty

You can do something like this:
while [ ! -s "$file" ] ; do sleep 1 ; done

While [test shows file either does not exist or is empty]
Do
Check again if file exists and if file is empty
Done

this is some kind of painfully loaded cycle, you don’t have to do that.