|Integer ASCII code:||4|
|Binary code:||0000 0100|
Unicode symbol: ␄, int code: 9220 (html ␄) hex code: 2404 (html ␄)
Frequently used on Unix in order to show end-of-file on a terminal.
End-of-Transmission character or shortly EOT is a transmission control character in telecommunication. Its main goal is to show the conclusion of a transmission that could have consisted of one or more texts as well as any related message headings.
Some other functions are triggered by EOT as well, for example releasing circuits, disconnecting terminals, or putting receive terminals in a backup condition. Nowadays it's often used in order to to cause a Unix terminal driver to signal end of file, this way exit programs that are awaiting input.
The character is encoded at U+0004 <control-0004> in ASCII and Unicode. It can be mentioned as Ctrl+D, ^D in caret notation. When EOT needs a graphic display, Unicode provides the character U+2404 ␄ SYMBOL FOR END OF TRANSMISSION (HTML ␄). Besides, U+2301 ⌁ ELECTRIC ARROW can be used as a graphic reflection of EOT; in Unicode it is mentioned as"symbol for End of Transmission".
One has to know, that EOT character in Unix and Control-Z in DOS are two different things. The DOS Control-Z byte's primer function is to send and/or place in files in order to show the end of the text. On the contrary, the Control-D makes the Unix terminal driver to signal the EOF condition. It is not a character, so the byte has no particular meaning if it is read or written from a file or terminal.
EOT character in Unix makes the terminal driver to immediately make all characters in its input buffer available. In any normal situation the driver would collect characters and stop doing it when see an end-of-line character. In case when the input buffer is empty (for the reason that no characters have been typed since the last end-of-line or end-of-file), a program reading from the terminal reads a count of zero bytes. Such a condition in Unix means nothing but having reached the end of the file.
The cat program on Unix-based operating systems, for example Linux, can show it pretty well: in order to begin, run the cat command. It will accept its input from the keyboard and print output to the screen. Type a few characters but don't press ↵ Enter. Finally type Ctrl+D. The characters typed to that point are sent to cat, which consequently writes them to the screen. The input stream can be considered to be finished and the program ends if Ctrl+D is typed without typing any characters first. A real EOT can be received by typing Ctrl+V then Ctrl+D.
The so - called "raw" mode of the terminal driver means, that it doesn't interpret control characters anymore, so the EOT character is sent to the program without any changes. The program may interpret it in any possible way. This way a program can consider the EOT byte as an indication that it should end the text; this would then be similar to how Ctrl+Z is handled by DOS programs.
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