UNIX for Dummies Questions & Answers

What is meant by "exit $?"

$? is bash shell exit status, include 0-255, 0 is successful.

what is the difference when i write "exit $?" and "exit" in a shell script

Without an argument it defaults to $? but this might not have always been the case, and besides, it's more explicit that way.

$? is the exit code of the previous process you invoked. So for example

Code:

grep fnord /etc/issue
exit $?

... will relay the exit code from grep as the exit code of the script which contains the grep command (or more generally of the current shell, but in a script, that's equivalent to the current script).

if the shell script only have "exit" not have any parameter, this script will return a code before the "exit" command.

#!/bin/bash
date
exit
this simple script will return the exit status of command "date".