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New HOWTO: Emacs Beginner's HOWTO - page 3

Table of Contents, Section 1

  • March 26, 2001
  3.  Emacs Modes

  Emacs modes are different behaviors and features which you can turn on
  or off (or customize, of course) for use in different circumstances.
  Modes are what make one editor (Emacs) equally useful for writing
  documentation, programming in a variety of languages (C, C++, Perl,
  Python, Java, and many more), creating a home page, sending E-Mail,
  reading Usenet news, keeping track of your appointments, and even
  playing games.

  Emacs modes are simply libraries of Lisp code that extend, modify, or
  enhance Emacs is some way.

  3.1.  Major vs. Minor Modes

  There are fundamentally two types of modes available: Major and Minor.
  The distinction isn't the easiest thing to grasp until you've worked
  with a few of them off and on, but let's give it a shot.

  Only one major mode can be active at a given time. Many minor modes
  can be active at a given time. Major modes tend to be language or
  task-specific, while minor modes are smaller and less specific
  utilities that cut across many tasks.

  Sounds kind of abstract, so let's try an example. There's a mode that
  I use quite often when I'm writing plain old text files. It's called
  text-mode. This mode was designed for writing free form text like a
  README file. It understands how to identify words and paragraphs and
  generally makes sure that it does what I expect when I use the normal
  navigation keystrokes.

  When I'm writing text for human consumption, I typically want it to
  look good. It should be properly word-wrapped to a reasonable value
  and so on. To enable word wrapping I just turn on the auto-fill minor
  mode. This mode tries to do the Right Thing when I'm typing along and
  hit the end of the line. The fact that it is a minor mode means that
  it can work with several different major modes. My notion of the
  ``Right Thing'' to do when I hit the end of the line is different when
  I'm in text-mode than it is when I'm in java-mode for example. I don't
  want my Java code to be word-wrapped as if was English text. But I do
  want the blocks of comments in my Java code to be word wrapped! auto-
  fill mode is smart enough to figure that out.

  The authors of various Emacs modes have done a great job of making
  sure that things that should work as minor modes are minor modes.

  If you look back at that ASCII sketch of an Emacs screen, you'll
  notice that the mode line identifies the mode(s) that Emacs is in. In
  that case it was in a mode called ``Lisp Interaction'' which is the
  default mode. It's really only useful if you're going to be writing
  Lisp code. (But since most of Emacs is written in Lisp, why not?)

  3.2.  Programming Modes

  First and foremost, Emacs was designed by a programmer for
  programmers. There are high-quality modes available for almost every
  popular programming language you can think of (and even some not so
  popular ones). I only briefly describe a few of them here.

  Most programming modes share some common characteristics. Usually,
  they'll do some or all of the following:

  �  Provide color-syntax highlighting for the language.

  �  Provide automatic indentation and code formatting for the language.

  �  Provide context (language) sensitive help.

  �  Automatically interface with your debugger.

  �  Add language-specific menus to the menu bar.

  In addition, there are some non-language specific modes that help out
  with tasks that are common to programming in many languages. Things
  like interfacing to your version control software, automatically
  adding comments to your code, creating Makefiles, updating Change Logs
  and so on.

  When you add all these modes together and consider the maturity and
  stability of the Emacs code, it compares quite nicely to commercially
  marketed Integrated Development Environments (IDEs) for languages like
  C++ and Java. And, of course, it's free.

  3.2.1.  C/C++/Java

  Because the syntax of C, C++, and Java are quite similar, there is one
  Emacs mode which handles all three languages (as well as Objective-C
  and IDL). It's a very mature and complete package and it included in
  the Emacs distribution. This mode is called either cc-mode or CC Mode.

  For more details or to download a newer version, visit
  http://www.python.org/emacs/.

  3.2.2.  Perl

  There are actually two modes for editing Perl code in Emacs. The first
  is called perl-mode (as you would expect) and the second is cperl-
  mode. I don't have a good grasp of this history and why there are two
  modes (the docs don't say), but it would appear that perl-mode was the
  original mode for editing Perl code in Emacs. It seems to have fewer
  features than cperl-mode and is lacking the ability to recognize some
  of Perl's fancier language constructs.

  Personally, I use and recommend cperl-mode which seems to be quite
  actively maintained and has just about every feature I could ever
  want. You can find the latest release here: ftp://ftp.math.ohio-
  state.edu/pub/users/ilya/emacs.

  But don't take my word for it. Try them both and pick the one that
  best meets your needs.

  3.2.3.  Python

  Python (another very popular scripting language) has an Emacs mode
  available for it as well. As far as I can tell, it is not distributed
  with GNU Emacs but it distributed with XEmacs. It works quite well in
  both editors, though.

  You can get python-mode from the official Python web site
  http://www.python.org/emacs/python-mode/.

  3.2.4.  Others

  There are many many other editing modes available to help out
  programmers. Such modes help out with things like:

  �  Shell Scripts (Bash, sh, ksh, csh, ...)

  �  Awk, Sed, Tcl, ...

  �  Makefiles

  �  Change Logs

  �  Documentation

  �  Debugging

  And much more. See the last section of this document for more
  information on finding other modes and add-ins.

  3.3.  Authoring

  Fancy Emacs modes are not limited to just those who write code. Folks
  writing documentation (of any sorts) can also benefit from a wide
  selection of Emacs modes.

  3.3.1.  Spell-Checking ( ispell  mode)

  Authors of many types of documents need to spell-check once in a
  while. If you have GNU ispell installed, you can type M-x ispell and
  spell-check the current buffer. If ispell finds words that it doesn't
  know, it prompts you with a list of possible replacements and lets you
  select one (or none) of them. It's functionally equivalent to the
  spell-checkers in many popular non-free software packages.

  3.3.2.  HTML ( html-helper  mode)

  If you find yourself writing HTML files once in a while (or even a
  lot), you might want to try out html-helper-mode. It is available from
  http://www.santafe.edu/~nelson/tools/ as is the documentation and
  related stuff.

  As its name suggests, html-helper-mode provides lots of things to help
  out those folks who still write HTML by hand--the old fashioned way.

  3.3.3.  TeX ( tex-mode )

  When you're writing documents in TeX, it's often helpful to get Emacs
  to add some color and highlight the backslashes, braces and other
  characters. tex-mode takes care of that for you.

  Though I don't write much directly in TeX anymore, when I did this
  mode proved to be quite helpful in making my TeX source a bit more
  readable.

  3.3.4.  SGML ( sgml-mode )

  The document you're now reading was written in SGML (and probably
  converted to the format you're reading it in). sgml-mode provides all
  the basics for SGML documents: validation, highlighting, forward-tag,
  backward-tag, and much more. It is a standard part of Emacs.

  3.4.  Other Modes

  Of course, there are lots of other handy modes to make life easier.
  Here's just a sampling of the popular ones:

  3.4.1.  Version Control ( vc  mode)

  vc mode interfaces with most of the popular version control back-ends
  (RCS, SCCS, CVS) to make it very easy to check files in and out,
  manage releases and so on. It is a standard part of Emacs and is
  documented in the Emacs documentation.

  3.4.2.  Shell Mode

  Why switch to another X window or virtual console just to run a few
  shell commands? Do it from within Emacs and save yourself the trouble.
  :-)

  M-x shell will launch a shell within an Emacs buffer. You can do most
  things with this buffer that you could do with a normal shell prompt
  (except for running full screen programs like vi or pine) because
  Emacs is talking to your real shell behind the scenes.

  This is a standard part of Emacs, too, so you'll find it documented in
  the Emacs docs.

  3.4.3.  Telnet and FTP

  Why switch to another X window or virtual console just to run telnet
  or FTP?  Do it from within Emacs and save yourself the trouble.
  (Notice the pattern yet?)

  Just like running a shell inside of Emacs, you can telnet and ftp. Try
  M-x telnet or M-x ftp to experience it for yourself. See the
  documentation for all the gory details.

  3.4.4.  Man

  Why switch to another X window or virtual console just to read a
  manual page?  Do it from within Emacs and save yourself the trouble.
  (I promise. I'll stop.)

  Just like running a shell inside of Emacs, you can read manual pages.
  Try M-x man to experience it for yourself. See the documentation for
  more.

  3.4.5.  Ange-FTP

  To quote the ange-ftp documentation:

       This package attempts to make accessing files and directo�
       ries using FTP from within GNU Emacs as simple and transpar�
       ent as possible.  A subset of the common file-handling rou�
       tines are extended to interact with FTP.

  That means you can treat files on remote machines as if there were
  local. So if you need to edit a file on a different computer, just
  tell Emacs to open it (using a slightly different path syntax) and it
  takes care of all the details of logging in and retrieving the file.
  Then, when you save the file via C-x C-s, ange-ftp intercepts the save
  and writes the file back to the remote machine.

  The slightly different path syntax goes like this... A file named
  ``myfile'', in a ``user'''s directory, on a machine named
  ``my.host.org'' can be opened by opening (C-x f) the file:

       /user@my.host.org:~user/myfile

  This, also, is a standard part of the Emacs distribution so you can
  find it documented in the Emacs documentation.

  Thanks to Etienne Grossmann (etienne@anonimo.isr.ist.utl.pt) for the
  example above.
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