End-of-Transmission character: Difference between revisions

Undid revision 636872968 by Vadmium (talk)Put comment back in, this is still broken on many Linux systems
(→‎Meaning in Unix: Revert bold → quotes; remove dumb self-link)
(Undid revision 636872968 by Vadmium (talk)Put comment back in, this is still broken on many Linux systems)
In Unix the end-of-file character (by default EOT) causes the terminal driver to make available all characters in its input buffer immediately; normally the driver would collect characters until it sees an end-of-line character. If the input buffer is empty (because 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. In Unix, such a condition is understood as having reached the end of the file.
 
This can be demonstrated with the <tt>[[cat (Unix)|cat]]</tt> program on [[Unix]]-based operating systems such as [[Linux]]: Run the <code>cat</code> command with no arguments, so it accepts its input from the keyboard and prints output to the screen. Type a few characters without pressing {{keypress|Enter}}, then type {{keypress|Ctrl|D}}. The characters typed to that point are sent to cat, which then writes them to the screen. If {{keypress|Ctrl|D}} is typed without typing any characters first, the input stream is terminated and the program ends. An actual EOT is obtained by typing {{keypress|Ctrl|V}} then {{keypress|Ctrl|D}}. The actual Unicode &#x2404; <!-- if this symbol does not appear as EOT the font used on your computer is faulty ie. ubuntu 12.04 suffers this and also incorrectly displays the ENQ glyph --> character [[glyph]] can be obtained by typing [[Unicode_input#In_X11_.28Linux_and_other_Unix_variants.29|{{keypress|Ctrl|Shift|U}}]] then {{keypress|2}} {{keypress|4}} {{keypress|0}} {{keypress|4}} {{keypress|Enter}}.
 
If the terminal driver is in "'''raw"''' mode, it no longer interprets control characters, and the EOT character is sent unchanged to the program, which is free to interpret it any way it likes. A program may then decide to handle the EOT byte as an indication that it should end the text, this would then be similar to how {{keypress|Ctrl|Z}} is handled by DOS programs.
 
== Usage in mainframe computer system communications protocols ==