Question

I saw the code written somewhere online, and I wanted to know what exactly does “$?” do/give us.
Googling did not help.

Here’s the code I saw it in:

#!/bin/sh

ping -c 2 localhost
if [ $? != 0 ] ; then
    echo "Couldn't ping localhost, weird"
    fi

ping -c 2 veryweirdhostname.noend 
if [ $? != 0 ] ; then
    echo "Surprise, Couldn't ping a very weird hostname.."
    fi

echo "The pid of this process is $$"

Taken from: http://efod.se/writings/linuxbook/html/shell-scripts.html

Answer 1

$? is a variable holding the return value of the last command you ran.

Example C program (example.c):

int main() { return 1; }

Example Bash:

gcc -o example example.c
./example
echo $? # prints 1