Editing End-of-file (section)

==EOF character==
Input from a terminal never really "ends" (unless the device is disconnected), but it is useful to enter more than one "file" into a terminal, so a key sequence is reserved to indicate end of input. In [[Unix|UNIX]], the translation of the keystroke to EOF is performed by the terminal driver, so a program does not need to distinguish terminals from other input files. By default, the driver converts a [[End-of-transmission character|Control-D]] character at the start of a line into an end-of-file indicator. To insert an actual Control-D (ASCII 04) character into the input stream, the user precedes it with a "quote" command character (usually [[Control-V]]). [[AmigaDOS]] is similar but uses Control-\ instead of Control-D.

In [[DOS]] and [[Microsoft Windows|Windows]] (and in [[CP/M]] and many [[Digital Equipment Corporation|DEC]] operating systems such as the [[PDP-6]] monitor,<ref name="DEC_1965_PDP-6"/> [[RT-11]], [[OpenVMS|VMS]] or [[TOPS-10]]<ref name="DEC_1970_PDP-10"/>), reading from the terminal will never produce an EOF. Instead, programs recognize that the source is a terminal (or other "character device") and interpret a given reserved character or sequence as an end-of-file indicator; most commonly, this is an [[ASCII]] [[Substitute character|Control-Z]], code 26. Some MS-DOS programs, including parts of the Microsoft MS-DOS shell ([[COMMAND.COM]]) and operating-system utility programs (such as [[EDLIN]]), treat a Control-Z in a text file as marking the end of meaningful data, and/or append a Control-Z to the end when writing a text file. This was done for two reasons:
* Backward compatibility with [[CP/M]]. The CP/M [[file system]] (and also the original [[8-bit FAT]] implemented in [[Microsoft BASIC]]) only recorded the lengths of files in multiples of 128-byte "records", so, by convention, a Control-Z character was used to mark the end of meaningful data if it ended in the middle of a record. The [[FAT12]] filesystem introduced with [[86-DOS]] and MS-DOS has always recorded the exact byte-length of files, so this was never necessary on DOS.
* It allows programs to use the same code to read input from both a terminal and a text file.

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In the ANSI X3.27-1969 [[magnetic tape data storage|magnetic tape]] standard, the end of file was indicated by a '''tape mark''', which consisted of a gap of approximately 3.5&nbsp;inches of tape followed by a single byte containing the character <code>0x13</code> (hex) for [[9-track tape|nine-track tapes]] and <code>017</code> (octal) for [[IBM 7-track|seven-track tapes]].<ref name="MARC21_1977"/> The '''end-of-tape''', commonly abbreviated as '''EOT''', was indicated by two tape marks. This was the standard used, for example, on [[IBM 360]]. The [[9-track tape#Technical details|reflective strip]] that was used to announce impending physical end of tape was also called an '''EOT''' marker.