what does '$?' mean in a shell script?

Question

I came across a shell script that contains a statement like,

if [ $val -eq $? ]

What does $? mean here?

Answer 1

What does $? mean here?

$? is the last result of an exit-status ... 0 is by default "successfull"

bash# ls *.*
bash# echo $? 
bash# 0
bash# ls /tmp/not/existing/
bash# echo $?
bash# 2