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Conditional Commands


When an internal command or external program finished, it returns a result 
called the exit code.  Conditional commands allow you to perform tasks 
based upon the previous command's exit code.  Many programs return a 0 if 
they are successful and a non-zero value if they encounter an error. 
If you separate two commands by && (AND), the second command will be 
executed only if the first returns an exit code of 0.  For example, the 
following command will only erase files if the BACKUP operation succeeds: 


        [c:\] backup c:\ a: && del c:\*.bak;*.lst

If you separate two commands by || (OR), the second command will be 
executed only if the first returns a non-zero exit code.  For example, if 
the following BACKUP operation fails, then ECHO will display a message: 


        [c:\] backup c:\ a: || echo Error in the backup!

All internal commands return an exit code, but not all external programs 
do.  Conditional commands will behave unpredictably if you use them with 
external programs which do not return an explicit exit code.  To determine 
whether a particular external program returns a meaningful exit code use 
an ECHO %? command immediately after the program is finished.  If the 
program's documentation does not discuss exit codes you may need to 
experiment with a variety of conditions to see how the exit code changes. 

Created using Inf-PHP v.2 (c) 2003 Yuri Prokushev
Created using Inf-HTML v.0.9b (c) 1995 Peter Childs