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Any program in the MS-DOS environment can set an exit value that can be detected with IF ERRORLEVEL. Any MS-DOS command can return a value, but only the above commands have exit codes defined in the MS-DOS specifications. Return values from other commands should not be relied upon, as they may be different for different versions and dialects of MS-DOS.

None of the internal MS-DOS commands have defined return codes. An external command is a separate MS-DOS program; internal commands are contained within COMMAND.COM and are always available for use when the MS-DOS prompt is active.

You can determine if a command is internal or external by checking your MS-DOS documentation. In MS-DOS 5.0 and 5.0a, commands are marked as internal or external in the chart that accompanies each command in Chapter 14 of the "Microsoft MS-DOS User's Guide and Reference" manual. Earlier versions of the manual include a boxed E or I symbol on the upper outside corner of the page to denote external or internal.

Customers have suggested that exit codes be defined for all appropriate MS-DOS commands (both internal and external). This feature is under review and will be considered for inclusion in a future release.