ls /oraarch/USUP/*.arc > /dev/null 2>&1
if [[ $? -eq 0 ]]
then
   /usr/bin/compress /oraarch/MOM/*.arc
   fi

You need to understand the theory first and then its upto you how and where you want to apply that theory. I'll try to explain above to you. The greater-than (>) in commands like these redirect the program’s output somewhere. In this case, something is being redirected into /dev/null, and something is being redirected into &1. Standard in, out and error: There are three standard sources of input and output for a program. Standard input usually comes from the keyboard if it’s an interactive program, or from another program if it’s processing the other program’s output. The program usually prints to standard output, and sometimes prints to standard error. These three file descriptors (you can think of them as “data pipes”) are often called STDIN, STDOUT, and STDERR. Sometimes they’re not named, they’re numbered! The built-in numberings for them are 0, 1, and 2, in that order. By default, if you don’t name or number one explicitly, you’re talking about STDOUT. That means file descriptor 0 or fd0 denotes STDIN or standard input and file descriptor 1 or fd1 denotes STDOUT or standard output and file descriptor 2 or fd2 denotes STDERR or standard error. You can see the command above is redirecting standard output into /dev/null, which is a place you can dump anything you don’t want (often called the bit-bucket), then redirecting standard error into standard output (you have to put an & in front of the destination when you do this). The short explanation, therefore, is “all output from this command should be shoved into a black hole.” That’s one good way to make a program be really quiet! Regards, Tayyab

The code does not dump any files into /dev/null. Lets have a look at it step by step:
1) ls /oraarch/USUP/*.arc lists all files in /oraarch/USUP with extension .arc to STDOUT
2) > /dev/null sends all what would go to STDOUT to nirvana, so you will not see any normal output of the ls-command
3) 2>&1 says STDERR should go to the same destination as STDOUT, so you will not see any errormessages from the ls-command
4) if [[ $? -eq 0 ]] $? holds the return code of the last command in your case the ls whose complete output was discarded. A return code of 0 means success. [[ ... ]] is the syntax for a condition and -eq inside such a construct means equal. Together this says if ls found any files do whats between then and fi .
5) /usr/bin/compress /oraarch/MOM/*.arc compress is used to ... compress files.

i have to say is clearer to me. But is there any link i can see some example like stdout, stderror.