jove.2

早期freebsd实现

.LP
The basic unit of stored data is the file.
Each program,
each paper,
lives usually in its own file.
To edit a program or paper,
the editor must be told the name of the file that contains it.
This is called \fIvisiting\fP a file.
To make your changes to the file permanent on disk,
you must \fIsave\fP the file.
.NH 2
Visiting Files
.XS \n(PN 5n
\*(SN Visiting Files
.XE
.LP
.IP "C-X C-V" 15n
Visit a file.
.IP "C-X C-R" 15n
Same as C-X C-V.
.IP "C-X C-S" 15n
Save the visited file.
.IP "ESC ~" 15n
Tell \s-2JOVE\s0 to forget that the buffer has been changed.
.LP
.LP
\fIVisiting\fP a file means copying its contents into \s-2JOVE\s0 where you
can edit them.
\s-2JOVE\s0 remembers the name of the file you visited.
Unless you use the multiple buffer feature of \s-2JOVE\s0,
you can only be visiting one file at a time.
The name of the current selected buffer is visible in the mode line.
.LP
The changes you make with \s-2JOVE\s0 are made in a copy inside \s-2JOVE\s0.
The file itself is not changed.
The changed text is not permanent until you \fIsave\fP it in a file.
The first time you change the text,
an asterisk appears at the end of the mode line; this indicates that the text
contains fresh changes which will be lost unless you save them.
.LP
To visit a file,
use the command C-X C-V.
Follow the command with the name of the file you wish to visit,
terminated by a Return.
You can abort the command by typing C-G,
or edit the filename with many of the standard \s-2JOVE\s0 commands
(e.g., C-A, C-E, C-F, ESC F, ESC Rubout).
If the filename you wish to visit is similar to the filename in the
mode line (the default filename),
you can type C-R to insert the default and then edit it.
If you do type a Return to finish the command,
the new file's text appears on the screen,
and its name appears in the mode line.
In addition,
its name becomes the new default filename.
.LP
If you wish to save the file and make your changes permanent,
type C-X C-S.
After the save is finished,
C-X C-S prints the filename and the
number of characters and lines that it wrote to the file.
If there are no changes to save (no asterisk at the end of the mode line),
the file is not saved;
otherwise the changes saved and the asterisk at the end of
the mode line will disappear.
.LP
What if you want to create a file?  Just visit it.
\s-2JOVE\s0 prints
\fI(New file)\fP but aside from that behaves as if you had visited an existing
empty file.
If you make any changes and save them,
the file is created.
If you visit a nonexistent file unintentionally
(because you typed the wrong filename),
go ahead and visit the file you meant.
If you don't save the unwanted file,
it is not created.
.LP
If you alter one file and then visit another in the same buffer,
\s-2JOVE\s0 offers to save the old one.
If you answer YES,
the old file is saved;
if you answer NO,
all the changes you have made to it since the last save are lost.
You should not type ahead after a file visiting
command,
because your type-ahead might answer an unexpected question
in a way that you would regret.
.LP
Sometimes you will change a buffer by accident.
Even if you undo the effect of the change by editing,
\s-2JOVE\s0 still knows that "the buffer has been changed".
You can tell \s-2JOVE\s0 to pretend that there have been no changes with the
ESC \s+2~\s0 command (\fImake-buffer-unmodified\fP).
This command simply clears the "modified" flag which
says that the buffer contains changes which need to be saved.
Even if
the buffer really \fIis\fP changed \s-2JOVE\s0 will still act as if it were not.
.LP
If \s-2JOVE\s0 is about to save a file and sees that the date of the version
on disk does not match what \s-2JOVE\s0 last read or wrote,
\s-2JOVE\s0 notifies you of this fact,
and asks what to do, because this probably means that something is wrong.
For example,
somebody else may have been editing the same file.
If this is so,
there is a good chance that your work
or his work will be lost if you don't take the proper steps.
You should first find out exactly what is going on.
If you determine that somebody else has modified the file,
save your file under a different filename and then DIFF the two files
to merge the two sets of changes.  (The "patch" command is useful for
applying the results of context diffs directly).
Also get in touch with the other person so that the files don't diverge
any further.
.NH 2
How to Undo Drastic Changes to a File
.XS \n(PN 5n
\*(SN How to Undo Drastic Changes to a File
.XE
.LP
If you have made several extensive changes to a file and then change
your mind about them,
and you haven't yet saved them,
you can get rid of them by reading in the previous version of the file.
You can do this with the C-X C-V command,
to visit the unsaved version of the file.
.NH 2
Recovering from system/editor crashes
.XS \n(PN 5n
\*(SN Recovering from system/editor crashes
.XE
.LP
JOVE does not have \fIAuto Save\fP mode, but it does provide a way to
recover your work in the event of a system or editor crash.  JOVE saves
information about the files you're editing every so many changes to a
buffer to make recovery possible.  Since a relatively small amount of
information is involved it's hardly even noticeable when JOVE does this.  The
variable "sync-frequency" says how often to save the necessary
information, and the default is every 50 changes.  50 is a very
reasonable number: if you are writing a paper you will not lose more than
the last 50 characters you typed, which is less than the average length
of a line.
.NH 2
Miscellaneous File Operations
.XS \n(PN 5n
\*(SN Miscellaneous File Operations
.XE
.LP
.LP
ESC X \fIwrite-file\fP <file><return> writes the contents of the buffer
into the file <file>,
and then visits that file.
It can be thought of as a way of "changing the name" of
the file you are visiting.
Unlike C-X C-S,
\fIwrite-file\fP saves even if the buffer has not been changed.
C-X C-W is another way of getting this command.
.LP
ESC X \fIinsert-file\fP <file><return> inserts the contents of <file> into the
buffer at point,
leaving point unchanged before the contents.
You can also use C-X C-I to get this command.
.LP
ESC X \fIwrite-region\fP <file><return> writes the region (the text between
point and mark) to the specified file.
It does not set the visited filename.
The buffer is not changed.
.LP
ESC X \fIappend-region\fP <file><return> appends the region to <file>.
The text is added to the end of <file>.
.NH 1
Using Multiple Buffers
.XS \n(PN
\*(SN Using Multiple Buffers
.XE
.LP
When we speak of "the buffer",
which contains the text you are editing,
we have given the impression that there is only one.
In fact,
there may be many of them,
each with its own body of text.
At any time only one buffer can be \fIselected\fP and available for editing,
but it isn't hard to switch to a different one.
Each buffer individually remembers which file it is visiting,
what modes are in effect,
and whether there are any changes that need saving.
.IP "C-X B" 15n
Select or create a buffer.
.IP "C-X C-F" 15n
Visit a file in its own buffer.
.IP "C-X C-B" 15n
List the existing buffers.
.IP "C-X K" 15n
Kill a buffer.
.LP
Each buffer in \s-2JOVE\s0 has a single name,
which normally doesn't change.
A buffer's name can be any length.
The name of the currently selected buffer
and the name of the file visited in it
are visible in the mode line when you are at top level.
A newly started \s-2JOVE\s0 has only one buffer,
named \fBMain\fP, unless you specified files to edit in the
shell command that started \s-2JOVE\s0.
.NH 2
Creating and Selecting Buffers
.XS \n(PN 5n
\*(SN Creating and Selecting Buffers
.XE
.LP
To create a new buffer,
you need only think of a name for it (say, FOO)
and then do C-X B FOO<return>,
which is the command C-X B (\fIselect-buffer\fP) followed by the name.
This makes a new,
empty buffer (if one by that name didn't previously exist) 
and selects it for editing.
The new buffer is not visiting any file,
so if you try to save it you will be asked for the filename to use.
Each buffer has its own major mode;
the new buffer's major mode is \fIText\fP mode by default.
.LP
To return to buffer FOO later after having switched to another,
the same command C-X B FOO<return> is used,
since C-X B can tell whether a buffer named FOO exists already or not.
C-X B Main<return> reselects the buffer Main that \s-2JOVE\s0 started out with.
Just C-X B<return> reselects the previous buffer.
Repeated C-X B<return>'s alternate between the last two buffers selected.
.LP
You can also read a file into its own newly created buffer,
all with one command: C-X C-F (\fIfind-file\fP),
followed by the filename.
The name of the buffer is the last element of the file's pathname.
C-F stands for "Find",
because if the specified file already resides in a buffer in your \s-2JOVE\s0,
that buffer is reselected.
So you need not remember whether you have brought the file in already or not.
A buffer created by C-X C-F can be reselected later with C-X B or C-X C-F,
whichever you find more convenient.
Nonexistent files can be created with C-X C-F just as they can with C-X C-V.
.NH 2
Using Existing Buffers
.XS \n(PN 5n
\*(SN Using Existing Buffers
.XE
.LP
To get a list of all the buffers that exist,
do C-X C-B (\fIlist-buffers\fP).
Each buffer's type,
name,
and visited filename is printed.
An asterisk before the buffer name indicates a
buffer which contains changes that have not been saved. The number
that appears at the beginning of a line in a C-X C-B listing is that
buffer's \fIbuffer number\fP.
You can select a buffer by typing its number in place of its name.
If a buffer with that number doesn't already exist,
a new buffer is created with that number as its name.
.LP
If several buffers have modified text in them,
you should save some of them with C-X C-M (\fIwrite-modified-files\fP).
This finds all the buffers that need saving and then saves them.
Saving the buffers this way is much
easier and more efficient (but more dangerous)
than selecting each one and typing C-X C-S.
If you give C-X C-M an argument, \s-2JOVE\s0 will ask for confirmation
before saving each buffer.
.LP
ESC X \fIrename-buffer\fP <new name><return> changes the name of the currently
selected buffer.
.LP
ESC X \fIerase-buffer\fP <buffer name><return> erases the contents of the
<buffer name> without deleting the buffer entirely.
.NH 2
Killing Buffers
.XS \n(PN 5n
\*(SN Killing Buffers
.XE
.LP
After you use a \s-2JOVE\s0 for a while,
it may fill up with buffers which you no longer need.
Eventually you can reach a point where trying to
create any more results in an "out of memory" or "out of lines"
error.
When this happens you will want to kill some buffers with the
C-X K (\fIdelete-buffer\fP) command.
You can kill the buffer FOO by doing C-X K FOO<return>.
If you type C-X K <return> JOVE will kill the previously selected buffer.
If you try to kill a buffer that needs saving \s-2JOVE\s0
will ask you to confirm it.
.LP
If you need to kill several buffers, use the command \fIkill-some-buffers\fP.
This prompts you with the name of each buffer and asks for confirmation
before killing that buffer.
.NH 1
Controlling the Display
.XS \n(PN
\*(SN Controlling the Display
.XE
.LP
Since only part of a large file will fit on the screen,
\s-2JOVE\s0 tries to show the part that is likely to be interesting.
The display control commands allow you to see a different part of the file.
.IP "C-L" 15n
Reposition point at a specified vertical position,
OR clear and redraw the screen with point in the same place.
.IP "C-V" 15n
Scroll forwards (a screen or a few lines).
.IP "ESC V" 15n
Scroll backwards.
.IP "C-Z" 15n
Scroll forward some lines.
.IP "ESC Z" 15n
Scroll backwards some lines.
.LP
.LP
The terminal screen is rarely large enough to display all of your
file.
If the whole buffer doesn't fit on the screen,
\s-2JOVE\s0 shows a contiguous portion of it,
containing 
.I point.
It continues to show approximately the same portion
until point moves outside of what is displayed;
then \s-2JOVE\s0 chooses a new portion centered around the new 
.I point.
This is \s-2JOVE\s0's guess as to what you are most interested in seeing,
but if the guess is wrong,
you can use the display control commands to see a different portion.
The available screen area through which you can see part of
the buffer is called \fIthe window\fP,
and the choice of where in the
buffer to start displaying is also called \fIthe window\fP.  (When 
there is only one window, it plus the mode line and the input line take
up the whole screen).
.LP
First we describe how \s-2JOVE\s0 chooses a new window position on its own.
The goal is usually to place 
.I point 
half way down the window.
This is controlled by the variable \fIscroll-step\fP,
whose value is the number of
lines above the bottom or below the top of the window that the line
containing point is placed.
A value of 0 (the initial value) means center 
.I point
in the window.
.LP
The basic display control command is C-L (\fIredraw-display\fP).
In its simplest form,
with no argument,
it tells \s-2JOVE\s0 to choose a new window position,
centering point half way from the top as usual.
.LP
C-L with a positive argument chooses a new window so as to put point
that many lines from the top.
An argument of zero puts point on the very top line.
Point does not move with respect to the text; rather,
the text and point move rigidly on the screen.
.LP
If point stays on the same line,
the window is first cleared and then redrawn.
Thus,
two C-L's in a row are guaranteed to clear the current window.
ESC C-L will clear and redraw the entire screen.
.LP
The \fIscrolling\fP commands C-V,
ESC V,
C-Z,
and ESC Z,
let you move the whole display up or down a few lines.
C-V (\fInext-page\fP) with an
argument shows you that many more lines at the bottom of the screen,
moving the text and point up together as C-L might.
C-V with a
negative argument shows you more lines at the top of the screen,
as does ESC V (\fIprevious-page\fP) with a positive argument.
.LP
To read the buffer a window at a time,
use the C-V command with no argument.
It takes the last line at the bottom of the window and puts
it at the top,
followed by nearly a whole window of lines not visible before.
Point is put at the top of the window.