DB-Access question

I have a question about DB-Access and any error codes it may or may not return. My employer is using a series of nested shell scripts to execute 4GL (well, 4ge in this case..) programs that unload rows from various tables if the rows are new or modified. The programs each build a temporary text file containing a large SQL statement, and then RUN DBACCESS <DATABASE> <SQLFILE> to acually execute the unload. The unload is the only step within the SQL statement in the respective temp file. One of these unloads blew up a few weeks ago while another automated process was changing the lock mode of one of the tables. The various programs and shell scripts were always expecting the unload portion of this process to be successful, so everything else chugged along. So I need to modify the shell scripts and programs to perform more error handling. In order to do this i need to know what statuses DB-Access returns, and how I can capture them. Any advice would be greatly appreciated. ->Dan