How to determine the exit status of a command executed on UNIX and Windows?

PROBLEM/ABSTRACT:
How to determine the exit status of a command executed on UNIX and Windows?

SOLUTION:
A return value of zero (0) indicates the command completed without error. A non zero value indicates the command failed. To determine the return value you will run the following command.

UNIX:
echo $?

Example:
# ls
foo.c
# echo $?
0
# ls -z
ls: invalid option -- z
Try `ls --help' for more information.
# echo $?
1

Windows:
echo %ERRORLEVEL%

Example:
C:\>dir
Volume in drive C has no label.
Volume Serial Number is 5C83-6C21

Directory of C:\

02/08/2006 11:49 AM <DIR> .
02/08/2006 11:49 AM <DIR> ..
01/18/2006 10:58 AM 57 foo.c

C:\>echo %ERRORLEVEL%
0

C:\>dir bar.c
Volume in drive C has no label.
Volume Serial Number is 5C83-6C21

Directory of C:\

File Not Found

C:\>echo %ERRORLEVEL%
1

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