I learned about the command line command test and read a few examples. One of them was obscure to me:
test 100 -gt 99 && echo "Yes, that's true." || echo "No, that's false."
I understand it to this point:
test 100 -gt 99
evaluates whether 100 is greater than 99
echo "Yes, that's true." || echo "No, that's false."
If the expression turns out to be true do the command on the left of the double pipe symbol, otherwise do the right one.
I could not find any hint onto the & expression in the manual.
What is its purpose?