EXIT status messages in NIX

Exit Status

By default in Linux if particular command/shell script is executed, it return two type of values which is used to see whether command or shell script executed is successful or not.

(1) If return value is zero (0), command is successful.
(2) If return value is nonzero, command is not successful or some sort of error executing command/shell script.

This value is know as Exit Status.

But how to find out exit status of command or shell script?
Simple, to determine this exit Status you can use $? special variable of shell.

For e.g. If I want to remove a non-existing file

$ rm ABCD
rm: cannot remove `ABCD': No such file or directory
and after that if you give command
$ echo $?
it will print nonzero value to indicate error. Now give command

$ ls
$ echo $?
It will print 0 to indicate command is successful.

Exercise
Try these exit status and check for yourself:

$ expr 1 + 3
$ echo $?

$ echo Welcome
$ echo $?

$ wildwest canwork?
$ echo $?

$ date
$ echo $?

$ echon $?
$ echo $?