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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
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Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 428
SEC. 5.6
USER INTERFACES: KEYBOARD, MOUSE, MONITOR
397
standard. The defaults are all control characters that should not conflict with text
input or codes used by programs; all except the last two can be changed under pro-
gram control.
Character
POSIX name
Comment
CTRL-H
ERASE
Backspace one character
CTRL-U
KILL
Erase entire line being typed
CTRL-V
LNEXT
Interpret next character literally
CTRL-S
STOP
Stop output
CTRL-Q
START
Start output
DEL
INTR
Interrupt process (SIGINT)
CTRL-\
QUIT
Force core dump (SIGQUIT)
CTRL-D
EOF
End of file
CTRL-M
CR
Carriage return (unchangeable)
CTRL-J
NL
Line feed (unchangeable)
Figure 5-31.
Characters that are handled specially in canonical mode.
The
ERASE
character allows the user to rub out the character just typed.
It is
usually the backspace (CTRL-H).
It is not added to the character queue but instead
removes the previous character from the queue.
It should be echoed as a sequence
of three characters, backspace, space, and backspace, in order to remove the previ-
ous character from the screen.
If the previous character was a tab, erasing it de-
pends on how it was processed when it was typed.
If it is immediately expanded
into spaces, some extra information is needed to determine how far to back up.
If
the tab itself is stored in the input queue, it can be removed and the entire line just
output again. In most systems, backspacing will only erase characters on the cur-
rent line.
It will not erase a carriage return and back up into the previous line.
When the user notices an error at the start of the line being typed in, it is often
convenient to erase the entire line and start again. The
KILL
character erases the
entire line. Most systems make the erased line vanish from the screen, but a few
older ones echo it plus a carriage return and line feed because some users like to
see the old line. Consequently, how to echo
KILL
is a matter of taste.
As with
ERASE
it is usually not possible to go further back than the current line. When a
block of characters is killed, it may or may not be worth the trouble for the driver
to return buffers to the pool, if one is used.
Sometimes the
ERASE
or
KILL
characters must be entered as ordinary data.
The
LNEXT
character serves as an
escape character
.
In UNIX CTRL-V is the de-
fault. As an example, older UNIX systems often used the @ sign for
KILL
, but the
Internet mail system uses addresses of the form
linda@cs.washington.edu
. Some-
one who feels more comfortable with older conventions might redefine
KILL
as @,
but then need to enter an @ sign literally to address email. This can be done by
typing CTRL-V @. The CTRL-V itself can be entered literally by typing CTRL-V
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