how to find out exit status of command or shell script?

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. (This example assumes that unkfile doest not exist on your hard drive)

$ rm unkfile
It will show error as follows
rm: cannot remove `unkowm1file': 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 the following commands and not down the exit status:
$ expr 1 + 3
$ echo $?

$ echo Welcome
$ echo $?

$ wildwest canwork?
$ echo $?

$ date
$ echo $?

$ echon $?
$ echo $?

Shell Built in Variables


Shell Built in Variables	Meaning
$#	Number of command line arguments. Useful to test no. of command line args in shell script.
$*	All arguments to shell
$@	Same as above
$-	Option supplied to shell
$$	PID of shell
$!	PID of last started background process (started with &)