This chapter contains several brief topics that do not fit anywhere else: reading netnews, running shell commands and shell subprocesses, using a single shared Emacs for utilities that expect to run an editor as a subprocess, printing hardcopy, sorting text, narrowing display to part of the buffer, editing double-column files and binary files, saving an Emacs session for later resumption, emulating other editors, various diversions and amusements.
GNUS is an Emacs subsystem for reading and responding to netnews. You can use GNUS to browse through news groups, look at summaries of articles in specific group, and read articles of interest. You can respond to authors or write replies to all the readers of a news group.
This section introduces GNUS and describes several basic features. For more information, run M-x info and select the GNUS manual.
To start GNUS, type M-x gnus RET.
GNUS creates and uses three Emacs buffers, each with its own particular purpose and its own major mode.
The Newsgroup buffer contains a list of newsgroups. This is the first buffer that GNUS displays when it starts up. Normally the list contains only the newsgroups to which you subscribe (which are listed in your `.newsrc' file) and which contain unread articles. Use this buffer to select a specific newsgroup.
The Summary buffer lists the articles in a single newsgroup, including their subjects, their numbers, and who posted them. GNUS creates a Summary buffer for a newsgroup when you select the group in the Newsgroup buffer. Use this buffer to select an article.
The Article buffer displays the text of an article. You rarely need to select this buffer because you can scroll through it while remaining in the Summary buffer.
At startup, GNUS reads your `.newsrc' news initialization file and attempts to communicate with the local news server, which is a repository of news articles. The news server need not be the same computer you are logged in on.
If you start GNUS and connect to the server, but do not see any newsgroups listed in the Newsgroup buffer, type L to get a listing of all the newsgroups. Then type u to unsubscribe from the newsgroups you don't want to read. (You can move point to a particular group using n and p or the usual Emacs commands.)
The first time you start GNUS, it subscribes automatically to every newsgroup that exists. Subsequently, GNUS subscribes automatically to all newly created newsgroups. You can unsubscribe groups with u. You can inhibit automatic subscription by adding the following line to your `~/.newsrc' file:
options -n !all !all.all
When you quit GNUS with q, it automatically records in your `.newsrc' initialization file the subscribed or unsubscribed status of all newsgroups, except for groups you have "killed". (You do not need to edit this file yourself, but you may.) When new newsgroups come into existence, GNUS subscribes to them automatically; if you don't want to read them, use u to unsubscribe from them.
Reading news is a two step process:
Each GNUS buffer has its own special commands, but commands that do the similar things have similar key bindings. Here are commands for the Newsgroup and Summary buffers:
Emacs has commands for passing single command lines to inferior shell processes; it can also run a shell interactively with input and output to an Emacs buffer named `*shell*'.
shell-command).
shell-command-on-region).
M-! (shell-command) reads a line of text using the
minibuffer executes it as a shell command in a subshell made just for
this command. Standard input for the command comes from the null
device. If the shell command produces any output, the output goes into
an Emacs buffer named `*Shell Command Output*', which is displayed
in another window but not selected. A numeric argument, as in M-1
M-!, directs this command to insert any output into the current
buffer. In that case, point is left before the output and the mark is
set after the output.
If the shell command line ends in `&', it runs asynchronously.
M-| (shell-command-on-region) is like M-! but
passes the contents of the region as the standard input to the shell
command, instead of no input. If a numeric argument is used, meaning
insert the output in the current buffer, then the old region is deleted
first and the output replaces it as the contents of the region.
Both M-! and M-| use shell-file-name to specify the
shell to use. This variable is initialized based on your SHELL
environment variable when Emacs is started. If the file name does not
specify a directory, the directories in the list exec-path are
searched; this list is initialized based on the environment variable
PATH when Emacs is started. Your `.emacs' file can override
either or both of these default initializations.
Both M-! and M-| wait for the shell command to complete.
To stop waiting, type C-g to quit; that terminates the shell
command with the signal SIGINT---the same signal that C-c
normally generates in the shell. Emacs waits until the command actually
terminates. If the shell command doesn't stop (because it ignores the
SIGINT signal), type C-g again; this sends the command a
SIGKILL signal which is impossible to ignore.
To run a subshell interactively, putting its typescript in an Emacs buffer, use M-x shell. This creates (or reuses) a buffer named `*shell*' and runs a subshell with input coming from and output going to that buffer. That is to say, any "terminal output" from the subshell goes into the buffer, advancing point, and any "terminal input" for the subshell comes from text in the buffer. To give input to the subshell, go to the end of the buffer and type the input, terminated by RET.
Emacs does not wait for the subshell to do anything. You can switch windows or buffers and edit them while the shell is waiting, or while it is running a command. Output from the subshell waits until Emacs has time to process it; this happens whenever Emacs is waiting for keyboard input or for time to elapse.
To make multiple subshells, rename the buffer `*shell*' to something different using M-x rename-uniquely. Then type M-x shell again to create a new buffer `*shell*' with its own subshell. If you rename this buffer as well, you can create a third one, and so on. All the subshells run independently and in parallel.
The file name used to load the subshell is the value of the variable
explicit-shell-file-name, if that is non-nil. Otherwise,
the environment variable ESHELL is used, or the environment
variable SHELL if there is no ESHELL. If the file name
specified is relative, the directories in the list exec-path are
searched; this list is initialized based on the environment variable
PATH when Emacs is started. Your `.emacs' file can override
either or both of these default initializations.
As soon as the subshell is started, it is sent as input the contents of the file `~/.emacs_shellname', if that file exists, where shellname is the name of the file that the shell was loaded from. For example, if you use bash, the file sent to it is `~/.emacs_bash'.
cd, pushd and popd commands given to the inferior
shell are watched by Emacs so it can keep the `*shell*' buffer's
default directory the same as the shell's working directory. These
commands are recognized syntactically by examining lines of input that are
sent. If you use aliases for these commands, you can tell Emacs to
recognize them also. For example, if the value of the variable
shell-pushd-regexp matches the beginning of a shell command line,
that line is regarded as a pushd command. Change this variable when
you add aliases for `pushd'. Likewise, shell-popd-regexp and
shell-cd-regexp are used to recognize commands with the meaning of
`popd' and `cd'. These commands are recognized only at the
beginning of a shell command line.
If Emacs gets an error while trying to handle what it believes is a
`cd', `pushd' or `popd' command, it runs the hook
shell-set-directory-error-hook (see section Hooks).
If Emacs does not properly track changes in the current directory of the subshell, use the command M-x dirs to ask the shell what its current directory is. This command works for shells that support the most common command syntax; it may not work for unusual shells.
Shell buffer use Shell mode, which defines several special keys attached to the C-c prefix. They are chosen to resemble the usual editing and job control characters present in shells that are not under Emacs, except that you must type C-c first. Here is a complete list of the special key bindings of Shell mode:
comint-send-input). When a line is
copied, any text at the beginning of the line that matches the variable
shell-prompt-pattern is left out; this variable's value should be
a regexp string that matches the prompts that your shell uses.
comint-dynamic-complete). TAB also completes history
references (see section Shell History References) and environment variable names.
The variable shell-completion-fignore specifies a list of file
name extensions to ignore in Shell mode completion. The default setting
ignores file names ending in `~', `#' or `%'. Other
related Comint modes use the variable comint-completion-fignore
instead.
comint-dynamic-list-filename-completions).
comint-delchar-or-maybe-eof). Typed at the end of the shell
buffer, C-d sends EOF to the subshell. Typed at any other
position in the buffer, C-d deletes a character as usual.
comint-bol).
comint-kill-input).
backward-kill-word).
comint-interrupt-subjob).
comint-stop-subjob).
comint-quit-subjob).
comint-kill-output). This is useful if a shell command spews
out lots of output that just gets in the way.
comint-show-output).
comint-show-maximum-output).
shell-forward-command). The variable shell-command-regexp
specifies how to recognize the end of a command.
shell-backward-command).
comint-dynamic-list-input-ring).
(add-hook 'comint-output-filter-functions
'comint-watch-for-password-prompt)
(add-hook 'comint-output-filter-functions
'comint-strip-ctrl-m)
comint-buffer-maximum-size.
Here's how to do this automatically each time you get output from the
subshell:
(add-hook 'comint-output-filter-functions
'comint-truncate-buffer)
Shell mode also customizes the paragraph commands so that only shell prompts start new paragraphs. Thus, a paragraph consists of an input command plus the output that follows it in the buffer.
Shell mode is a derivative of Comint mode, a general purpose mode for communicating with interactive subprocesses. Most of the features of Shell mode actually come from Comint mode, as you can see from the command names listed above. The specialization of Shell mode in particular include the choice of regular expression for detecting prompts, the directory tracking feature, and a few user commands.
Other Emacs features that use variants of Comint mode include GUD (see section Running Debuggers Under Emacs) and M-x run-lisp (see section Running an External Lisp).
You can use M-x comint-run to execute any program of your choice in a subprocess using unmodified Comint mode--without the specializations of Shell mode.
Shell buffers support three ways of repeating earlier commands. You can use the same keys used in the minibuffer; these work much as they do in the minibuffer, inserting text from prior commands while point remains always at the end of the buffer. You can move through the buffer to previous inputs in their original place, then resubmit them or copy them to the end. Or you can use a `!'-style history reference.
Shell buffers provide a history of previously entered shell commands. To reuse shell commands from the history, use the editing commands M-p, M-n, M-r and M-s. These work just like the minibuffer history commands except that they operate on the text at the end of the shell buffer, where you would normally insert text to send to the shell.
M-p fetches an earlier shell command to the end of the shell buffer. Successive use of M-p fetches successively earlier shell commands, each replacing any text that was already present as potential shell input. M-n does likewise except that it finds successively more recent shell commands from the buffer.
The history search commands M-r and M-s read a regular expression and search through the history for a matching command. Aside from the choice of which command to fetch, they work just like M-p and M-r. If you enter an empty regexp, these commands reuse the same regexp used last time.
When you find the previous input you want, you can resubmit it by typing RET, or you can edit it first and then resubmit it if you wish.
These commands get the text of previous shell commands from a special history list, not from the shell buffer itself. Thus, editing the shell buffer, or even killing large parts of it, does not affect the history that these commands access.
Some shells store their command histories in files so that you can refer to previous commands from previous shell sessions. Emacs reads the command history file for your chosen shell, to initialize its own command history. The file name is `~/.bash_history' for bash, `~/.sh_history' for ksh, and `~/.history' for other shells.
comint-previous-prompt).
comint-next-prompt).
comint-copy-old-input). This is useful if you
move point back to a previous command. After you copy the command, you
can submit the copy as input with RET. If you wish, you can
edit the copy before resubmitting it.
Moving to a previous input and then copying it with C-c RET produces the same results--the same buffer contents--that you would get by using M-p enough times to fetch that previous input from the history list. However, C-c RET copies the text from the buffer, which can be different from what is in the history list if you edit the input text in the buffer after it has been sent.
Various shells including csh and bash support history references that begin with `!' and `^'. Shell mode can understands these constructs and perform the history substitution for you. If you insert a history reference and type TAB, this searches the input history for a matching command, performs substitution if necessary, and places the result in the buffer in place of the history reference. For example, you can fetch the most recent command beginning with `mv' with ! m v TAB. You can edit the command if you wish, and then resubmit the command to the shell by typing RET.
History references take effect only following a shell prompt. The
variable shell-prompt-pattern specifies how to recognize a shell
prompt. Comint modes in general use the variable
comint-prompt-regexp to specify how to find a prompt; Shell mode
uses shell-prompt-pattern to set up the local value of
comint-prompt-regexp.
Shell mode can optionally expand history references in the buffer when
you send them to the shell. To request this, set the variable
comint-input-autoexpand to input.
You can make SPC perform history expansion by binding SPC to
the command comint-magic-space.
If the variable comint-scroll-to-bottom-on-input is
non-nil, insertion and yank commands scroll the selected window
to the bottom before inserting.
If comint-scroll-show-maximum-output is non-nil, then
scrolling due to arrival of output tries to place the last line of text
at the bottom line of the window, so as to show as much useful text as
possible. (This mimics the scrolling behavior of many terminals.)
The default is nil.
By setting comint-scroll-to-bottom-on-output, you can opt for
having point jump to the end of the buffer whenever output arrives--no
matter where in the buffer point was before. If the value is
this, point jumps in the selected window. If the value is
all, point jumps in each window that shows the comint buffer. If
the value is other, point jumps in all nonselected windows that
show the current buffer. The default value is nil, which means
point does not jump to the end.
The variable comint-input-ignoredups controls whether successive
identical inputs are stored in the input history. A non-nil
value means to omit an input that is the same as the previous input.
The default is nil, which means to store each input even if it is
equal to the previous input.
Three variables customize file name completion. The variable
comint-completion-addsuffix controls whether completion inserts a
space or a slash to indicate a fully completed file or directory name
(non-nil means do insert a space or slash).
comint-completion-recexact, if non-nil, directs TAB
to choose the shortest possible completion if the usual Emacs completion
algorithm cannot add even a single character.
comint-completion-autolist, if non-nil, says to list all
the possible completions whenever completion is not exact.
The command comint-dynamic-complete-variable does variable name
completion using the environment variables as set within Emacs. The
variables controlling file name completion apply to variable name
completion too. This command is normally available through the menu
bar.
Command completion normally considers only executable files.
If you set shell-command-execonly to nil,
it considers nonexecutable files as well.
You can configure the behavior of `pushd'. Variables control
whether `pushd' behaves like `cd' if no argument is given
(shell-pushd-tohome), pop rather than rotate with a numeric
argument (shell-pushd-dextract), and only add directories to the
directory stack if they are not already on it
(shell-pushd-dunique). The values you choose should match the
underlying shell, of course.
Emacs provides two commands for logging in to another computer and communicating with it through an Emacs buffer.
Use M-x telnet to set up a Telnet connection to another computer. (Telnet is the standard Internet protocol for remote login.) It reads the host name of the other computer as an argument with the minibuffer. Once the connection is established, talking to the other computer works like talking to a subshell: you can edit input with the usual Emacs commands, and send it a line at a time by typing RET. The output is inserted in the Telnet buffer interspersed with the input.
Use M-x rlogin to set up an Rlogin connection. Rlogin is
another remote login communication protocol, essentially much like the
Telnet protocol but incompatible with it, and supported only by certain
systems. Rlogin's advantages are that you can arrange not to have to
give your user name and password when communicating between two machines
you frequently use, and that you can make an 8-bit-clean connection.
(To do that in Emacs, set rlogin-explicit-args to ("-8")
before you run Rlogin.)
M-x rlogin sets up the default file directory of the Emacs buffer to access the remote host via FTP (see section File Names), and it tracks the shell commands that change the current directory just like Shell mode.
Various programs such as mail can invoke your choice of editor
to edit a particular piece of text, such as a message that you are
sending. By convention, most of these programs use the environment
variable EDITOR to specify which editor to run. If you set
EDITOR to `emacs', they invoke Emacs--but in an
inconvenient fashion, by starting a new, separate Emacs process. This
is inconvenient because it takes time and because the new Emacs process
doesn't share the buffers in the existing Emacs process.
You can arrange to use your existing Emacs process as the editor for
programs like mail by using the Emacs client and Emacs server
programs. Here is how.
First, the preparation. Within Emacs, call the function
server-start. (Your `.emacs' file can do this automatically
if you add the expression (server-start) to it.) Then, outside
Emacs, set the EDITOR environment variable to `emacsclient'.
(Note that some programs use a different environment variable; for
example, to make TeX use `emacsclient', you should set the
TEXEDIT environment variable to `emacsclient +%d %s'.)
Then, whenever any program invokes your specified EDITOR
program, the effect is to send a message to your principal Emacs telling
it to visit a file. (That's what the program emacsclient does.)
Emacs displays the buffer immediately and you can immediately begin
editing it.
When you've finished editing that buffer, type C-x #
(server-edit). This saves the file and sends a message back to
the emacsclient program telling it to exit. The programs that
use EDITOR wait for the "editor" (actually, emacsclient)
to exit. C-x # also checks for other pending external requests
to edit various files, and selects the next such file.
You can switch to a server buffer manually if you wish; you don't have to arrive at it with C-x #. But C-x # is the only way to say that you are "finished" with one.
If you set the variable server-window to a window or a frame,
C-x # displays the server buffer in that window or in that frame.
While mail or another application is waiting for
emacsclient to finish, emacsclient does not read terminal
input. So the terminal that mail was using is effectively
blocked for the duration. In order to edit with your principal Emacs,
you need to be able to use it without using that terminal. There are
two ways to do this:
mail and the principal Emacs in two
separate windows. While mail is waiting for emacsclient,
the window where it was running is blocked, but you can use Emacs by
switching windows.
mail;
then, emacsclient blocks only the subshell under Emacs, and you
can still use Emacs to edit the file.
Some programs write temporary files for you to edit. After you edit
the temporary file, the program reads it back and deletes it. If the
Emacs server is later asked to edit the same file name, it should assume
this has nothing to do with the previous occasion for that file name.
The server accomplishes this by killing the temporary file's buffer when
you finish with the file. Use the variable
server-temp-file-regexp to specify which files are temporary in
this sense; its value should be a regular expression that matches file
names that are temporary.
The Emacs commands for making hardcopy let you print either an entire buffer or just part of one, either with or without page headers. See also the hardcopy commands of Dired (see section Miscellaneous File Operations) and the diary (see section Commands Displaying Diary Entries).
print-buffer but print only the current region.
lpr-buffer but print only the current region.
The hardcopy commands (aside from the Postscript commands) pass extra
switches to the lpr program based on the value of the variable
lpr-switches. Its value should be a list of strings, each string
an option starting with `-'. For example, to use a printer named
`nearme', set lpr-switches like this:
(setq lpr-switches '("-Pnearme"))
The variable lpr-header-switches similarly specifies the extra
switches to use to make page headers. The variable
lpr-add-switches controls whether to supply `-T' and
`-J' options for the printer program: nil means don't do so.
The variable lpr-command specifies the name of the printer
program to run; the default value depends on your operating system type.
These commands convert buffer contents to Postscript, either printing it or leaving it in another Emacs buffer.
The Postscript commands, ps-print-buffer and
ps-print-region, print buffer contents in Postscript form. One
command prints the entire buffer; the other, just the region. The
corresponding `-with-faces' commands,
ps-print-buffer-with-faces and ps-print-region-with-faces,
use Postscript features to show the faces (fonts and colors) in the text
properties of the text being printed.
If you are using a color display, you can print a buffer of program
code with color highlighting by turning on Font-Lock mode in that
buffer, and using ps-print-buffer-with-faces.
All four of the commands above use the variables ps-lpr-command
and ps-lpr-switches to specify how to print the output.
ps-lpr-command specifies the command name to run, and
ps-lpr-switches specifies command line options to use. If you
don't set these variables yourself, they take their initial values from
lpr-command and lpr-switches.
The variable ps-print-header controls whether these commands
add header lines to each page--set it to nil to turn headers
off. You can turn off color processing by setting
ps-print-color-p to nil. Many other customization
variables for these commands are defined and described in the Lisp file
`ps-print.el'.
The commands whose names have `spool' instead of `print' generate the Postscript output in an Emacs buffer instead of sending it to the printer.
Emacs provides several commands for sorting text in the buffer. All operate on the contents of the region (the text between point and the mark). They divide the text of the region into many sort records, identify a sort key for each record, and then reorder the records into the order determined by the sort keys. The records are ordered so that their keys are in alphabetical order, or, for numeric sorting, in numeric order. In alphabetic sorting, all upper case letters `A' through `Z' come before lower case `a', in accord with the ASCII character sequence.
The various sort commands differ in how they divide the text into sort records and in which part of each record is used as the sort key. Most of the commands make each line a separate sort record, but some commands use paragraphs or pages as sort records. Most of the sort commands use each entire sort record as its own sort key, but some use only a portion of the record as the sort key.
For example, if the buffer contains this:
On systems where clash detection (locking of files being edited) is implemented, Emacs also checks the first time you modify a buffer whether the file has changed on disk since it was last visited or saved. If it has, you are asked to confirm that you want to change the buffer.
applying M-x sort-lines to the entire buffer produces this:
On systems where clash detection (locking of files being edited) is implemented, Emacs also checks the first time you modify a buffer saved. If it has, you are asked to confirm that you want to change the buffer. whether the file has changed on disk since it was last visited or
where the upper case `O' sorts before all lower case letters. If you use C-u 2 M-x sort-fields instead, you get this:
implemented, Emacs also checks the first time you modify a buffer saved. If it has, you are asked to confirm that you want to change the buffer. On systems where clash detection (locking of files being edited) is whether the file has changed on disk since it was last visited or
where the sort keys were `Emacs', `If', `buffer', `systems' and `the'.
M-x sort-columns requires more explanation. You specify the columns by putting point at one of the columns and the mark at the other column. Because this means you cannot put point or the mark at the beginning of the first line to sort, this command uses an unusual definition of `region': all of the line point is in is considered part of the region, and so is all of the line the mark is in, as well as all the lines in between.
For example, to sort a table by information found in columns 10 to 15,
you could put the mark on column 10 in the first line of the table, and
point on column 15 in the last line of the table, and then run
sort-columns. Equivalently, you could run it with the mark on
column 15 in the first line and point on column 10 in the last line.
This can be thought of as sorting the rectangle specified by point and the mark, except that the text on each line to the left or right of the rectangle moves along with the text inside the rectangle. See section Rectangles.
Many of the sort commands ignore case differences when comparing, if
sort-fold-case is non-nil.
Narrowing means focusing in on some portion of the buffer, making the rest temporarily inaccessible. The portion which you can still get to is called the accessible portion. Canceling the narrowing, which makes the entire buffer once again accessible, is called widening. The amount of narrowing in effect in a buffer at any time is called the buffer's restriction.
Narrowing can make it easier to concentrate on a single subroutine or paragraph by eliminating clutter. It can also be used to restrict the range of operation of a replace command or repeating keyboard macro.
narrow-to-region).
widen).
narrow-to-page).
When you have narrowed down to a part of the buffer, that part appears to be all there is. You can't see the rest, you can't move into it (motion commands won't go outside the accessible part), you can't change it in any way. However, it is not gone, and if you save the file all the inaccessible text will be saved. The word `Narrow' appears in the mode line whenever narrowing is in effect.
The primary narrowing command is C-x n n (narrow-to-region).
It sets the current buffer's restrictions so that the text in the current
region remains accessible but all text before the region or after the region
is inaccessible. Point and mark do not change.
Alternatively, use C-x n p (narrow-to-page) to narrow
down to the current page. See section Pages, for the definition of a page.
The way to cancel narrowing is to widen with C-x n w
(widen). This makes all text in the buffer accessible again.
You can get information on what part of the buffer you are narrowed down to using the C-x = command. See section Cursor Position Information.
Because narrowing can easily confuse users who do not understand it,
narrow-to-region is normally a disabled command. Attempting to use
this command asks for confirmation and gives you the option of enabling it;
if you enable the command, confirmation will no longer be required for
it. See section Disabling Commands.
Two-column mode lets you conveniently edit two side-by-side columns of text. It uses two side-by-side windows, each showing its own buffer.
There are three ways to enter two-column mode:
2C-two-columns). If the right-hand buffer doesn't already
exist, it starts out empty; the current buffer's contents are not
changed.
This command is appropriate when the current buffer is empty or contains
just one column and you want to add another column.
2C-split). The current
buffer becomes the left-hand buffer, but the text in the right-hand
column is moved into the right-hand buffer. The current column
specifies the split point. Splitting starts with the current line and
continues to the end of the buffer.
This command is appropriate when you have a buffer that already contains
two-column text, and you wish to separate the columns temporarily.
2C-associate-buffer).
f2 s or C-x 6 s looks for a column separator which is a string that appears on each line between the two columns. You can specify the width of the separator with a numeric argument to f2 s; that many characters, before point, constitute the separator string. By default, the width is 1, so the column separator is the character before point.
When a line has the separator at the proper place, f2 s puts the text after the separator into the right-hand buffer, and deletes the separator. Lines that don't have the column separator at the proper place remain unsplit; they stay in the left-hand buffer, and the right-hand buffer gets an empty line to correspond. (This is the way to write a line which "spans both columns while in two-column mode": write it in the left-hand buffer, and put an empty line in the right-hand buffer.)
The command C-x 6 RET or f2 RET
(2C-newline) inserts a newline in each of the two buffers at
corresponding positions. This is the easiest way to add a new line to
the two-column text while editing it in split buffers.
When you have edited both buffers as you wish, merge them with f2 1 or
C-x 6 1 (2C-merge). This copies the text from the right-hand
buffer as a second column in the other buffer. To go back to two-column
editing, use f2 s.
Use f2 d or C-x 6 d to disassociate the two buffers, leaving
each as it stands (2C-dissociate). If the other buffer, the one not
current when you type f2 d, is empty, f2 d kills it.
There is a special major mode for editing binary files: Hexl mode. To use it, use M-x hexl-find-file instead of C-x C-f to visit the file. This command converts the file's contents to hexadecimal and lets you edit the translation. When you save the file, it is converted automatically back to binary.
You can also use M-x hexl-mode to translate an existing buffer into hex. This is useful if you visit a file normally and then discover it is a binary file.
Ordinary text characters overwrite in Hexl mode. This is to reduce the risk of accidentally spoiling the alignment of data in the file. There are special commands for insertion. Here is a list of the commands of Hexl mode:
hexl-mode.
You can use the Desktop library to save the state of Emacs from one session to another. Saving the state means that Emacs starts up with the same set of buffers, major modes, buffer positions, and so on that the previous Emacs session had.
To use Desktop, you should first add these lines to your `.emacs' file, preferably at or near the end:
(load "desktop") (desktop-load-default) (desktop-read)
Then, to enable state saving in a particular Emacs session, use the command M-x desktop-save. Once you have done this, the state of this Emacs session will be saved when you exit Emacs.
In order for Emacs to recover the state from a previous session, you must start it with the same current directory as you used when you started the previous session.
The variable desktop-files-not-to-save controls which files are
excluded from state saving. Its value is a regular expression that
matches the files to exclude. By default, remote (ftp-accessed) files
are excluded; this is because visiting them again in the subsequent
session would be slow. If you want to include these files in state
saving, set desktop-files-not-to-save to "^$".
A recursive edit is a situation in which you are using Emacs
commands to perform arbitrary editing while in the middle of another
Emacs command. For example, when you type C-r inside of a
query-replace, you enter a recursive edit in which you can change
the current buffer. On exiting from the recursive edit, you go back to
the query-replace.
Exiting the recursive edit means returning to the unfinished
command, which continues execution. The command to exit is C-M-c
(exit-recursive-edit).
You can also abort the recursive edit. This is like exiting,
but also quits the unfinished command immediately. Use the command
C-] (abort-recursive-edit) to do this. See section Quitting and Aborting.
The mode line shows you when you are in a recursive edit by displaying square brackets around the parentheses that always surround the major and minor mode names. Every window's mode line shows this, in the same way, since being in a recursive edit is true of Emacs as a whole rather than any particular window or buffer.
It is possible to be in recursive edits within recursive edits. For
example, after typing C-r in a query-replace, you may type a
command that enters the debugger. This begins a recursive editing level
for the debugger, within the recursive editing level for C-r.
Mode lines display a pair of square brackets for each recursive editing
level currently in progress.
Exiting the inner recursive edit (such as, with the debugger c command) resumes the command running in the next level up. When that command finishes, you can then use C-M-c to exit another recursive editing level, and so on. Exiting applies to the innermost level only. Aborting also gets out of only one level of recursive edit; it returns immediately to the command level of the previous recursive edit. If you wish, you can then abort the next recursive editing level.
Alternatively, the command M-x top-level aborts all levels of recursive edits, returning immediately to the top level command reader.
The text being edited inside the recursive edit need not be the same text that you were editing at top level. It depends on what the recursive edit is for. If the command that invokes the recursive edit selects a different buffer first, that is the buffer you will edit recursively. In any case, you can switch buffers within the recursive edit in the normal manner (as long as the buffer-switching keys have not been rebound). You could probably do all the rest of your editing inside the recursive edit, visiting files and all. But this could have surprising effects (such as stack overflow) from time to time. So remember to exit or abort the recursive edit when you no longer need it.
In general, we try to minimize the use of recursive editing levels in GNU Emacs. This is because they constrain you to "go back" in a particular order--from the innermost level toward the top level. When possible, we present different activities in separate buffers so that you can switch between them as you please. Some commands switch to a new major mode which provides a command to switch back. These approaches give you more flexibility to go back to unfinished tasks in the order you choose.
GNU Emacs can be programmed to emulate (more or less) most other editors. Standard facilities can emulate these:
vi-mode command.
vip-mode as
it is with vi-mode because terminating insert mode does
not use it.
For full information, see the long comment at the beginning of the
source file, which is `lisp/vip.el' in the Emacs distribution.
M-x dissociated-press is a command for scrambling a file of text either word by word or character by character. Starting from a buffer of straight English, it produces extremely amusing output. The input comes from the current Emacs buffer. Dissociated Press writes its output in a buffer named `*Dissociation*', and redisplays that buffer after every couple of lines (approximately) so you can read the output as it comes out.
Dissociated Press asks every so often whether to continue generating output. Answer n to stop it. You can also stop at any time by typing C-g. The dissociation output remains in the `*Dissociation*' buffer for you to copy elsewhere if you wish.
Dissociated Press operates by jumping at random from one point in the buffer to another. In order to produce plausible output rather than gibberish, it insists on a certain amount of overlap between the end of one run of consecutive words or characters and the start of the next. That is, if it has just printed out `president' and then decides to jump to a different point in the file, it might spot the `ent' in `pentagon' and continue from there, producing `presidentagon'.(4) Long sample texts produce the best results.
A positive argument to M-x dissociated-press tells it to operate character by character, and specifies the number of overlap characters. A negative argument tells it to operate word by word and specifies the number of overlap words. In this mode, whole words are treated as the elements to be permuted, rather than characters. No argument is equivalent to an argument of two. For your againformation, the output goes only into the buffer `*Dissociation*'. The buffer you start with is not changed.
Dissociated Press produces nearly the same results as a Markov chain based on a frequency table constructed from the sample text. It is, however, an independent, ignoriginal invention. Dissociated Press techniquitously copies several consecutive characters from the sample between random choices, whereas a Markov chain would choose randomly for each word or character. This makes for more plausible sounding results, and runs faster.
It is a mustatement that too much use of Dissociated Press can be a developediment to your real work. Sometimes to the point of outragedy. And keep dissociwords out of your documentation, if you want it to be well userenced and properbose. Have fun. Your buggestions are welcome.
If you are a little bit bored, you can try M-x hanoi. If you are considerably bored, give it a numeric argument. If you are very very bored, try an argument of 9. Sit back and watch.
If you want a little more personal involvement, try M-x gomoku, which plays the game Go Moku with you.
M-x blackbox and M-x mpuz are two kinds of puzzles.
blackbox challenges you to determine the location of objects
inside a box by tomography. mpuz displays a multiplication
puzzle with letters standing for digits in a code that you must
guess--to guess a value, type a letter and then the digit you think it
stands for.
M-x dunnet runs an adventure-style exploration game, which is a bigger sort of puzzle.
When you are frustrated, try the famous Eliza program. Just do M-x doctor. End each input by typing RET twice.
When you are feeling strange, type M-x yow.