The $? is called exit code of an application used to run. As an example type following commands in console:
then press CTRL-Z and then type:
You will see 147 as the answer. Return values more than 128 usually means signal and you have to do the calculation by subtracting 128 from the returned result. In this case you will get 19 which means
You can read about linux signals using :
man 7 signal
My chief interest is software engineering, mainly dealing with Linux and Java projects, but also interested in teaching what I’ve learned, have published a couple of CBTs about programming in Persian (java/Android) and here I’ll share my thoughts and experiences in English as well.