Editing COMMAND.COM (section)

==Redirection, piping, and chaining==
Because DOS is a single-tasking operating system, [[Pipeline (software)|piping]] is achieved by running commands sequentially, redirecting to and from a [[temporary file]].{{Citation needed|date=March 2024}} COMMAND.COM makes no provision for redirecting the [[Standard streams#Standard error (stderr)|standard error]] channel.{{Citation needed|date=March 2024}}

; <code>''command'' < ''filename''</code> : Redirect [[Standard streams#Standard input (stdin)|standard input]] from a file or device
; <code>''command'' > ''filename''</code> : Redirect [[Standard streams#Standard output (stdout)|standard output]], overwriting target file if it exists.
; <code>''command'' >> ''filename''</code> : Redirect [[Standard streams#Standard output (stdout)|standard output]], appending to target file if it exists.
; <code>''command1'' | ''command2''</code> : Pipe [[Standard streams#Standard output (stdout)|standard output]] from ''command1'' to [[Standard streams#Standard input (stdin)|standard input]] of ''command2''
; <code>''command1'' ¶ ''command2''</code> :
: Commands separated by ASCII-20 (¶, invoked by {{keypress|Ctrl|T}}) are executed in sequence (chaining of commands).<ref name="Paul_1997_NWDOSTIP"/> In other words, first ''command1'' is executed until termination, then ''command2''.<ref name="Paul_1997_NWDOSTIP"/> This is an undocumented feature in COMMAND.COM of [[MS-DOS 5.0|MS-DOS]]/[[PC DOS 5.0]]<!-- tested MS-DOS 6.2 and PC DOS 7 --> and higher.<ref name="Paul_1997_NWDOSTIP"/> It is also supported by COMMAND.COM<!-- but not by CMD --> of the Windows NT family<!-- tested Windows XP --> as well as by DR-DOS 7.07. All versions of DR-DOS COMMAND.COM<!-- since 3.xx --> already supported a similar internal function utilizing an exclamation mark (!) instead (a feature originally derived from [[Concurrent DOS]] and [[Multiuser DOS]]) - in the single-user line this feature was only available internally (in built-in startup scripts like "!DATE!TIME") and indirectly through [[DOSKEY]]'s $T parameter to avoid problems with ! as a valid filename character.<ref name="Paul_1997_NWDOSTIP"/> [[4DOS]] supports a configurable command line separator ([[4DOS.INI]] CommandSep= or SETDOS /C), which defaults to ^.<ref name="4DOS_8.00_HELP"/> COMMAND.COM in newer versions of Windows NT<!-- works for example in XP, but not in MS-DOS/PC DOS COMMAND.COM --> also supports an {{code|&}} separator for compatibility with the cmd syntax in OS/2 and the Windows NT family.<ref name="4DOS_8.00_HELP"/> (cmd does not support the ¶ separator.)