Re: OT What does RET (Enter) do and how does it do it ??
- From: Rick Stevens <rstevens@xxxxxxxxxxxx>
- Date: Fri, 24 Aug 2007 16:38:02 -0700
On Fri, 2007-08-24 at 18:52 -0400, William Case wrote:
Thanks Rick;
I put your answer together with Alan's and I think I get a satisfying
answer.
On Fri, 2007-08-24 at 15:09 -0700, Rick Stevens wrote:
On Fri, 2007-08-24 at 17:42 -0400, William Case wrote:[snip]
Hi;
This question is meant as a Friday afternoon to a Sunday evening
discussion. It is not rush; but I have been unable to discover an answer
to what seems to me a basic question on how my computer works.
Well, it's simple. The intent of text editors, word processors and theTo re-summarize, the meaning of RET is established by the program being
like is that whatever you type in gets saved in the file. In *nix-ish
operating systems (Linux, Unix, MacOS, etc.), the RETURN or ENTER key is
denoted by a single character in the file. We call this the "newline"
character, which is the hexadecimal value 0x0a. In ASCII parlance,
that's the "LF" or "linefeed" character. The LF character can also
be entered by holding down the "CTRL" key and pressing "j" (also
sometimes called "control-J").
In Windows-type stuff (DOS, Windows, CP/M, etc.), the ENTER key is
denoted by a two character sequence, the hex value 0x0d (ASCII "CR" or
"carriage return"), followed by the hex value 0x0a (ASCII "LF" or
"linefeed" again). We call this sequence the "CRLF" sequence. Note
that the "CR" character can also be entered by holding down the "CTRL"
key and pressing "m", which is why it's sometimes called "control-M".
(ADDITIONAL INFO: The hex value of "m" is "0x4d" and that of "j" is
0x4a. Holding down the CTRL key inhibits the generation of bit 6 or
the value of 0x40, so CTRL-M generates 0x0d instead of 0x4d. Easy.)
So much for text editors, word processors and the like. Now, when
you're at a command prompt or other program requesting input (remember
that the command prompt is the shell program asking for input), the
RETURN (or ENTER) key signals the end of user input and the program then
processes that according to whatever the program is supposed to do.
Does that clarify things?
used. The program can create it's own meaning for RET; or use a
standardized meaning according to what has been bound to the keymap the
program is using, or redefine the keymap it uses to bind one or another
meaning to a key press or event.
That's pretty much it in a nutshell. Generally, RET (ENTER) is used to
signify the end of a line. What the program _does_ with that line is
up to the program.
I was also trying to emphasize that command prompts are really another
program (on *nix, the shell; on DOS/Windows, command.com or whatever
Windows calls it now) asking for input.
----------------------------------------------------------------------
- Rick Stevens, Principal Engineer rstevens@xxxxxxxxxxxx -
- CDN Systems, Internap, Inc. http://www.internap.com -
- -
- Silence! Or I shall replace you with a very small shell script! -
- - The Wizard of OS -
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- From: William Case
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