Name the file you want to look for in the lookup command:
If the file already exists, lookup will not report any error.
If the file does not exist, lookup will report the error:
err0 will contain the error code 3: "file not found."
lookup can be useful whenever you need to determine whether a file exists on the local system. You can lookup files to transfer, log files to append to, script files to execute, macro files for loading macros, files that you don't want to accidentally overwrite, and so on.