doc/en/tutorials/devel/devel.sgml

<!DOCTYPE linuxdoc PUBLIC "-//FreeBSD//DTD linuxdoc//EN">

<!--
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  ++ file: /home/james/docs/devel.sgml
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  ++ Copyright James Raynard, Thursday 30th May 1996
  ++
  ++ Sgml doc for programming under FreeBSD.
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<article>

<title>A User's Guide to FreeBSD Programming Tools
<author>James Raynard, <tt /jraynard@freebsd.org/
<date>30th May 1996

<abstract>

This document is an introduction to using some of the programming
tools supplied with FreeBSD, although much of it will be applicable to
many other versions of Unix. It does <it /not/ attempt to describe
coding in any detail. Most of the document assumes little or no
previous programming knowledge, although it is hoped that most
programmers will find something of value in it

</abstract>

<sect><heading>Introduction</heading>
<p>

FreeBSD offers an excellent development environment. Compilers for C,
C++, and Fortran and an assembler come with the basic system, not to
mention a Perl interpreter and classic Unix tools such as sed and awk.
If that isn't enough, there are many more compilers and interpreters
in the Ports collection. FreeBSD is very compatible with standards
such as POSIX and ANSI C, as well with its own BSD heritage, so it is
possible to write applications that will compile and run with little
or no modification on a wide range of platforms.
<p>
However, all this power can be rather overwhelming at first if you've
never written programs on a Unix platform before. This document aims
to help you get up and running, without getting too deeply into more
advanced topics. The intention is that this document should give you
enough of the basics to be able to make some sense of the
documentation.
<p>
Most of the document requires little or no knowledge of programming,
although it does assume a basic competence with using Unix and a
willingness to learn!

<sect><heading>Introduction to Programming</heading>
<p>
A program is a set of instructions that tell the computer to do
various things; sometimes the instruction it has to perform depends on
what happened when it performed a previous instruction. This section
gives an overview of the two main ways in which you can give these
instructions, or ``commands'' as they're usually called. One way uses
an interpreter, the other a compiler. As human languages are too
difficult for a computer to understand in an unambiguous way, commands
are usually written in one or other languages specially designed for
the purpose.

<sect1><heading>Interpreters</heading>
<p>
With an interpreter, the language comes as an environment, where you
type in commands at a prompt and the environment executes them for
you. For more complicated programs, you can type the commands into a
file and get the interpreter to load the file and execute the commands
in it. If anything goes wrong, many interpreters will drop you into a
debugger to help you track down the problem.
<P>
The advantage of this is that you can see the results of your commands
immediately, and mistakes can be corrected readily. The biggest
disadvantage comes when you want to share your programs with
someone. They must have the same interpreter (or you must have some
way of giving it to them) and they need to understand how to use
it. Also users may not appreciate being thrown into a debugger if they
press the wrong key! From a performance point of view, interpreters
can use up a lot of memory, and generally do not generate code as
efficiently as compilers.
<p>
In my opinion, interpreted languages are the best way to start if you
haven't done any programming before. This kind of environment is
typically found with languages like Lisp, Smalltalk, Perl and
Basic. It could also be argued that the Unix shell (sh, csh) is itself
an interpreter, and many people do in fact write shell `scripts' to
help with various ``housekeeping'' tasks on their machine. Indeed,
part of the original Unix philosophy was to provide lots of small
utility programs that could be linked together in shell scripts to
perform useful tasks.
<p>
<sect1><heading>Interpreters available with FreeBSD</heading>
<p>
Here is a list of interpreters that are available as <htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/" name="FreeBSD
packages">, with a brief discussion of some of the more popular
interpreted languages. 
<p>
To get one of these packages, all you need to do is to click on the
hotlink for the package, then run

<tscreen><verb>
       pkg_add <package name>
</verb></tscreen>

as root. Obviously, you'll need to have a fully-functional FreeBSD
2.1.0 system for the package to work!

<descrip>
<tag>Basic</tag>

Short for Beginner's All-purpose Symbolic Instruction Code. Developed
in the 1950s for teaching University students to program and provided
with every self-respecting personal computer in the 1980s, BASIC has
been the first programming language for many programmers. It's also
the foundation for Visual Basic.

The <htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/bwbasic-2.10.tgz"
name="Bywater Basic Interpreter"> and the <htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/pbasic-2.0.tgz"
name="Phil Cockroft's Basic Interpreter"> (formerly Rabbit Basic) are
available as FreeBSD <htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/" name="FreeBSD
packages">

<tag>Lisp</tag>

A language that was developed in the late 1950s as an alternative to
the ``number-crunching'' languages that were popular at the time.
Instead of being based on numbers, Lisp is based on `lists'; in fact
the name is short for "List Processing". Very popular in AI
(Artificial Intelligence) circles.

Lisp is an extremely powerful and sophisticated language, but can be
rather large and unwieldy. 

FreeBSD has <htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/gcl-2.0.tgz" name="GNU
Common Lisp"> available as a package.

<tag>Perl</tag>

Very popular with system administrators for writing scripts; also
often used on World Wide Web servers for writing CGI scripts.

Version 4, which is probably still the most widely-used version, comes
with FreeBSD; the newer
<htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/perl-5.001.tgz"
name="Perl Version 5"> is available as a package.

<tag>Scheme</tag>

A dialect of Lisp that is rather more compact and cleaner than Common
Lisp. Popular in Universities as it's simple enough to teach to
undergraduates as a first language, while it has a high enough level
of abstraction to be used in research work.

FreeBSD has packages of the 
<htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/elk-3.0.tgz" 
name="Elk Scheme Interpreter">, the 
<htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/mit-scheme-7.3.tgz"
name="MIT Scheme Interpreter"> and the 
<htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/scm-4e1.tgz"
name="SCM Scheme Interpreter">.
<!--
<tag>TCL and Tk</tag>

Programming with the X windowing system can best be described as
rather character-forming.  As someone once said, if they designed cars
the way X was designed, each car would have five steering wheels, all
following completely different conventions, but you can use the
radio-cassette player to change gears, which is a really useful
feature when you think about it. Or perhaps not.
<p>
Fortunately, it doesn't have to be like that. A number of people have
written "toolkits" for X, where all the interaction with X is hidden
inside toolkit routines and you can just say, in effect, ``pop up a
window and draw a line from point A to point B''. Many of these are
`libraries' that have to be called from inside a C program, but one of
the best known toolkits, John Ousterhout's Tk, provides a
straightforward way to write GUI programs using a scripted
language. And by one of those remarkable coincidences, he also happens
to have written an embeddable language, TCL (Tool Command Language)
which is very suitable for the purpose, although it is possible to use
other interpreted languages such as Perl or Scheme to send commands to
Tk.

FreeBSD has a <htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/tcl-7.4.2.tgz"
name="Tool Command Language"> package.
-->
<tag>Icon</tag>

<htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/icon-9.0.tgz"
name="The Icon Programming Language">.

<tag>Logo</tag>

<htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/ucblogo-3.3.tgz"
name="Brian Harvey's LOGO Interpreter">.

<tag>Python</tag>
<htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/python-1.2"
name="The Python Object-Oriented Programming Language">

</descrip>

<sect1><heading>Compilers</heading>
<p>
Compilers are rather different. First of all, you write your code in a
file (or files) using an editor. You then run the compiler and see if
it accepts your program. If it didn't compile, grit your teeth and go
back to the editor; if it did compile and gave you a program, you can
run it either at a shell command prompt or in a debugger to see if it
works properly. (If you run it in the shell, you may get a core dump).
<p>
Obviously, this is not quite as direct as using an interpreter.
However it allows you to do a lot of things which are very difficult
or even impossible with an interpreter, such as writing code which
interacts with the operating system - or even writing your own
operating system! It's also useful if you need to write very efficient
code, as the compiler can take its time and optimise the code, which
wouldn't be acceptable in an interpreter. And distributing a program
written for a compiler is usually more straightforward than one
written for an interpreter - you can just give them a copy of the
executable (assuming they have the same operating system as you).
<p>
Compiled languages include Pascal, C and C++. C and C++ are rather
unforgiving languages, and best suited to more experienced
programmers; Pascal, on the other hand, was designed as an educational
language, and is quite a good language to start with. Unfortunately,
FreeBSD doesn't have any Pascal support, except for a Pascal-to-C
converter in the ports.
<p>
As the edit-compile-run-debug cycle is rather tedious when using
separate programs, many commercial compiler makers have produced
Integrated Development Environments (IDEs for short). FreeBSD doesn't
have an IDE as such; however it's possible to use Emacs for this
purpose. This is discussed under Emacs.

<sect><heading>Compiling with cc</heading>
<p>
This section deals only with the GNU compiler for C and C++, since
that comes with the base FreeBSD system. It can be invoked by either
`cc' or `gcc'. The details of producing a program with an interpreter
vary considerably between interpreters, and are usually well covered
in the documentation and on-line help for the interpreter.
<p>
Once you've written your masterpiece, the next step is to convert it
into something that will (hopefully!) run on FreeBSD. This usually
involves several steps, each of which is done by a separate program.

<enum>

<item> Pre-process your source code to remove comments and do other
tricks like expanding `macros' in C.

<item> Check the syntax of your code to see if you have obeyed the
rules of the language. If you haven't, it will complain!

<item> Convert the source code into assembler - this is very close to
machine code, but still understandable by humans. Allegedly.  (To be
strictly accurate, cc converts the source code into its own,
machine-independent p-code instead of assembler at this stage).

<item> Convert the assembler into machine code - yep, we're talking
bits and bytes, ones and zeros here.

<item> Check that you've used things like functions and global
variables in a consistent way (eg if you've called a non-existent
function, it'll complain).

<item> If you're trying to produce an executable from several source
code files, work out how to fit them all together.

<item> Work out how to produce something that the system's run-time
loader will be able to load into memory and run.

<item> (Finally!) Write the executable on the file system.
</enum>

The word ``compiling'' is often used to refer to just steps 1 to 4 -
the others are referred to as ``linking''. Sometimes step 1 is
referred to as ``pre-processing'' and steps 3-4 as ``assembling''.
<p>
Fortunately, almost all this detail is hidden from you, as cc is a
front end that manages calling all these programs with the right
arguments for you; simply typing

<tscreen><verb>
       cc foobar.c
</verb></tscreen>

will cause foobar.c to be compiled by all the steps above. If you have
more than one file to compile, just do something like

<tscreen><verb>
       cc foo.c bar.c
</verb></tscreen>

Note that the syntax checking is just that - checking the syntax. It
won't check for any logical mistakes you may have made, like putting
the program into an infinite loop, or using a bubble sort when you
meant to use a binary sort. {In case you didn't know, a
binary sort is an efficient way of sorting things into order and a
bubble sort isn't.}
<p>
There are lots and lots of options for cc, which are all in the man
page.  Here are a few of the most important ones, with examples of how
to use them.

<descrip>
<tag/-o/
    The output name of the file. If you don't use this option, cc will 
    produce an executable called `a.out' (the reasons for this are buried
    in the mists of history).

    Example:-
<tscreen><verb>
       cc foobar.c           executable is a.out
       cc -o foobar foobar.c executable is foobar
</verb></tscreen>

<tag/-c/
    Just compile the file, don't link it. Useful for toy programs where
    you just want to check the syntax, or if you're using a Make file.

    Example:-

<tscreen><verb>
       cc -c foobar.c
</verb></tscreen>

    This will produce an ``object file'' (not an executable) called
    `foobar.o'. This can be linked together with other object files
    into an executable.

<tag/-g/

    Create a debug version of the executable. This makes the compiler
    put information into the executable about which line of which
    source file corresponds to which function call. A debugger can use
    this information to show the source code as you step through the
    program, which is <it /very/ useful; the disadvantage is that all
    this extra information makes the program much bigger. Normally,
    you compile with -g while you're developing a program and then
    compile a ``release version'' without -g when you're satisfied it
    works properly.

    Example:-

<tscreen><verb>
       cc -g foobar.c
</verb></tscreen>

    This will produce a debug version of the program. (Note, we didn't use
    the -o flag to specify the executable name, so we'll get an executable
    called `a.out'. Producing a debug version called `foobar' is left as an
    exercise for the reader!)

<tag/-O/
    Create an optimised version of the executable. The compiler performs
    various clever tricks to try and produce an executable that runs faster
    than normal. You can add a number after the `O' to specify a higher
    level of optimisation, but this often exposes bugs in the compiler's
    optimiser. For instance, the version of cc that comes with the 2.1.0
    release of FreeBSD is known to produce bad code with the `-O2'
    option in some circumstances.

    Optimisation is usually only turned on when compiling a release version.

    Example:-

<tscreen><verb>
       cc -O -o foobar foobar.c
</verb></tscreen>

    This will produce an optimised version of `foobar'.
<p>
    The following three flags will force cc to check that your code
    complies to the relevant international standard (often referred to
    as the ``ANSI'' standard, though strictly speaking it's an ISO
    standard).

<tag/-Wall/
    Enable all the warnings which the authors of cc believe are
    worthwhile. Despite the name, it will not enable all the warnings
    cc is capable of.

<tag/-ansi/
    Turn off most (but not all) of the non-standard features provided
    by cc. Despite the name, it does not guarantee strictly that your
    code will comply to the standard.

<tag/-pedantic/
    Turn off <it /all/ cc's non-standard features.
<p>
    Without these flags, cc will allow you to use some of its
    non-standard extensions to the standard. Some of these are very
    useful, but will not work with other compilers - in fact, one of
    the main aims of the standard is to allow people to write code
    that will work with any compiler on any system. (This is known as
    ``portable code'').
<p>
    Generally, you should try to make your code as portable as
    possible, as otherwise you may have to completely re-write the
    program later to get it to work somewhere else - and who knows
    what you may be using in a few years time?

    Example:-
<tscreen><verb>
       cc -Wall -ansi -pedantic -o foobar foobar.c
</verb></tscreen>
    will produce an executable `foobar' after checking foobar.c for standard
    compliance.

<tag/-l/
    Specify a library to be used during when linking.
<p>
    The most common example of this is when compiling a program that
    uses some of the mathematical functions in C. Unlike most other
    platforms, these are in a separate library from the standard C one
    and you have to tell the compiler to add it.
<p>
    The rule is that if the library is called `libsomething.a', you
    give cc the argument `-lsomething'. For example, the maths library
    is `libm.a', so you give cc the argument `-lm'. A common
    ``gotcha'' with the maths library is that it has to be the last
    library on the command line.
<p>
    Example:-
<tscreen><verb>
       cc -o foobar foobar.c -lm
</verb></tscreen>
    will link the maths library functions into `foobar'.
<p>
    If you're compiling C++ code, you need to add `-lg++' to the
    command line argument, to link the C++ library functions.
    Alternatively, you can run c++ instead of cc, which does this for
    you.
<p>
    Example:-
<tscreen><verb>
       cc -o foobar foobar.cc -lg++
       c++ -o foobar foobar.cc
</verb></tscreen>
    will both produce an executable `foobar' from the C++ source file
    `foobar.cc'. Note that, on Unix systems, C++ source files
    traditionally end in `.C', `.cxx' or `.cc', rather than the
    DOS-style `.cpp' (which was already used for something else). gcc
    used to rely on this to work out what kind of compiler to use on
    the source file; however, this restriction no longer applies, so
    you may now call your C++ files `.cpp' with impunity!
    {c++ can also be invoked as g++ on FreeBSD.}
</descrip>

<sect1><heading>Common cc Queries and Problems</heading>
<p>
Q. I'm trying to write a program which uses the sin() function and I get
   an error like this. What does it mean?

<tscreen><verb>
       /var/tmp/cc0143941.o: Undefined symbol `_sin' referenced from text segment
</verb></tscreen>

A. When using mathematical functions like sin(), you have to tell cc to link
   in the maths library, like so:-
<tscreen><verb>
       cc -o foobar foobar.c -lm
</verb></tscreen>
Q. All right, I wrote this simple program to practice using -lm. All
it does is raise 2.1 to the power of 6.
<code>
#include <stdio.h>

int main() {
	float f;

	f = pow(2.1, 6);
	printf("2.1 ^ 6 = %f\n", f);
	return 0;
}
</code>
and I compiled it as

<tscreen><verb>
gcc temp.c -lm
</verb></tscreen>

like you said I should, but I get this when I run it:-
<tscreen><verb>
$ ./a.out
2.1 ^ 6 = 1023.000000
</verb></tscreen>

This is <it /not/ the right answer! What the %$&#'s going on?
<p>
A. When the compiler sees you call a function, it checks if it's
already seen a prototype for it. If it hasn't, it assumes the function
returns an int, which is definitely not what you want here.
<p>
Q. So how do I fix this?
<p>
A. The prototypes for the mathematical functions are in math.h. If you
include this file, the compiler will be able to find the prototype and
it'll stop doing strange things to your calculation!

<code>
#include <math.h>
#include <stdio.h>

int main() {
...
</code>
<p>
<tscreen><verb>
$ ./a.out
2.1 ^ 6 = 85.766121
</verb></tscreen>

Morale: if you're using any of the mathematical functions, always
include math.h and remember to link in the maths library.

Q. I've compiled a file called `foobar.c' and I can't find an executable
   called `foobar'. Where's it gone?
<p>
A. cc will call the executable `a.out' unless you tell it differently. Use
   the -o option, eg
<tscreen><verb>
       cc -o foobar foobar.c
</verb></tscreen>
Q. OK, I've got an executable called `foobar', I can see it when I do
   `ls', but when I type in 'foobar' at the command prompt it tells me
   there's no such file. Why can't it find it?
<p>
A. Unlike DOS, Unix won't look in the current directory when it's
   trying to find out which executable you want it to run, unless you
   tell it to. Either type `./foobar', which means ``run the file
   called `foobar' in the current directory'', or change your PATH
   environment variable so that it looks something like
<tscreen><verb>
       bin:/usr/bin:/usr/local/bin:.
</verb></tscreen>
   (The dot at the end means ``look in the current directory if it's not in
    any of the others'')
<p>
Q. I called my executable `test', but nothing happens when I run
   it. What's going on?
<p>
A. Most Unix systems have a program called `test' in /usr/bin and the
   shell's picking that one up before it gets to checking the current
   directory. Either type 

<tscreen><verb>
       ./test
</verb></tscreen>

 or choose a better name for your program!
<p>
Q. I compiled my program and it seemed to run all right at first, then
   there was an error and it said something about ``core
   dumped''. What does that mean?
<p>
A. The name ``core dump'' dates back to the very early days of Unix,
   when the machines used core memory for storing data. Basically, if
   the program failed under certain conditions, the system would write
   the contents of core memory to disk in a file called ``core'',
   which the programmer could then pore over to find out what went
   wrong.
<p>
Q. Fascinating stuff, but what I am supposed to do now?
<p>
A. Use gdb to analyse the core (see Debugging).
<p>
Q. When my program dumped core, it said something about a segmentation
   fault. What's that?
<p>
A. This basically means that your program tried to perform some sort
   of illegal operation on memory; Unix is designed to protect the
   operating system and other programs from ``rogue'' programs.
<p>
   Common causes for this are:-
<itemize>
	<item> Trying to write to a NULL pointer, eg
<code>
		char *foo = NULL;
		strcpy(foo, "bang!");
</code>
	<item> Using a pointer that hasn't been initialised, eg
<code>
		char *foo;
		strcpy(foo, "bang!");
</code>
	   The pointer will have some random value that, with luck,
	   will point into an area of memory that isn't available to
	   your program and the kernel will kill your program before
	   it can do any damage. If you're unlucky, it'll point
	   somewhere inside your own program and corrupt one of your
	   data structures, causing the program to fail mysteriously.
<p>
	<item> Trying to access past the end of an array, eg
<code>
		int bar[20];
		bar[27] = 6;
</code>
	<item> Trying to store something in read-only memory, eg
<code>
		char *foo = "My string";
		strcpy(foo, "bang!");
</code>
	   (Unix compilers often put string literals like ``My string'' into
	   read-only areas of memory).

	<item> Doing naughty things with malloc() and free(), eg
<code>
		char bar[80];
		free(bar);
</code>
	   or
<code>
		char *foo = malloc(27);
		free(foo);
		free(foo);
</code>
</itemize>
	(Note making one of these mistakes will not always lead to an
	error, but they are always bad practice. Some systems and
	compilers are more tolerant than others, which is why programs
	that ran well on one system can crash when you try them on an
	another)
<p>
Q. Sometimes when I get a core dump it says ``bus error''. It says in
   my Unix book that this means a hardware problem, but the computer
   still seems to be working. Is this true?
<p>
A. No, fortunately not (unless of course you really do have a hardware
   problem...). This is usually another way of saying that you
   accessed memory in a way you shouldn't have.
<p>
Q. This dumping core business sounds as though it could be quite
   useful, if I can make it happen when I want to. Can I do this, or
   do I have to wait until there's an error?
<p>
A. Yes, just go to another console or xterm, do 

<tscreen><verb>
       ps
</verb></tscreen>

to find out the process ID of your program, and do

<tscreen><verb>
       kill -ABRT <pid>
</verb></tscreen>

   This is useful if your program has got stuck in an infinite loop,
   for instance. (If your program traps SIGABRT, there are several
   other signals which have a similar effect).

<sect><heading>Make</heading>
<p>
<sect1><heading>What is make?</heading>
<p>
When you're working on a simple program with only one or two source
files, typing in 

<tscreen><verb>
       cc file1.c file2.c
</verb></tscreen>

is not too bad, but it quickly becomes very tedious when there are
several files - and it can take a while to compile, too.
<p>
One way to get around this is to use object files and only recompile
the source file if the source code has changed. So we could have
something like:-

<tscreen><verb>
       cc file1.o file2.o ... file37.c ...
</verb></tscreen>

if we'd changed file37.c, but not any of the others, since the last
time we compiled.
<p>
This may speed up the compilation quite a bit, but doesn't solve the
typing problem.
<p>
Or we could write a shell script to solve the typing problem, but it
would have to re-compile everything, making it very inefficient on a
large project.
<p>
What happens if we have hundreds of source files lying about? What if
we're working in a team with other people who forget to tell us when
they've changed one of their source files that we use?
<p>
Perhaps we could put the two solutions together and write something
like a shell script that would contain some kind of magic rule saying
when a source file needs compiling. Now all we need now is a program
that can understand these rules, as it's a bit too complicated for the
shell.
<p>
This program is called <tt /make/. It reads in a file, called a make
file, that tells it how different files depend on each other, and
works out which files need to be re-compiled and which ones don't. For
example, a rule could say something like ``if fromboz.o is older than
fromboz.c, that means someone must have changed fromboz.c, so it needs
to be re-compiled.'' The make file also has rules telling make <it
/how/ to re-compile the source file, making it a much more powerful
tool.
<p>
Make files are typically kept in the same directory as the source they
apply to, and can be called `makefile', `Makefile' or `MAKEFILE'. Most
programmers use the name 'Makefile', as this puts it near the top of a
directory listing, where it can easily be seen (they don't use the
`MAKEFILE' form as block capitals are often used for documentation
files like `README').

<sect1><heading>Example of using make</heading>
<p>
Here's a very simple make file:-
<tscreen><verb>
foo: foo.c
	cc -o foo foo.c
</verb></tscreen>
It consists of two lines, a dependency line and a creation line.
<p>
The dependency line here consists of the name of the program (known as
``the target''), followed by a colon, then a gap, then the name of the
source file. When make reads this line, it looks to see if `foo'
exists; if it exists, it compares the time 'foo' was last modified to
the time `foo.c' was last modified. If 'foo' does not exist, or is
older than `foo.c', it then looks at the creation line to find out
what to do. In other words, this is the rule for working out when
foo.c needs to be re-compiled.
<p>
The creation line starts with a tab (press the tab key) and then the
command you would type to create `foo' if you were doing it at a
command prompt. If `foo' is out of date, or does not exist, `make'
then executes this command to create it. In other words, this is the
rule which tells make how to re-compile foo.c.
<p>
So, when you type `make', it will make sure that `foo' is up to date
with respect to your latest changes to `foo.c'. This principle can be
extended to Makefiles with hundreds of targets - in fact, on FreeBSD,
it is possible to compile the entire operating system just by typing
`make world' in the appropriate directory!
<p>
Another useful property of make files is that the targets don't have
to be programs. For instance, we could have a make file that looks
like this:-

<tscreen><verb>
foo: foo.c
	cc -o foo foo.c

install:
	cp foo /home/me
</verb></tscreen>

We can tell make which target we want to make by typing 

<tscreen><verb>
       make <target>
</verb></tscreen>

make will then only look at that target and ignore any
others. For example, if we type `make foo' with the make file above,
make will ignore the 'install' target.
<p>
If we just type `make' on its own, make will always look at the first
target and then stop without looking at any others. So if we typed
`make' here, it will just go to the `foo' target, re-compile `foo' if
necessary, and then stop without going on to the `install' target.
<p>
Notice that the `install' target doesn't actually depend on anything!
This means that the command on the following line is always executed
when we try to make that target by typing `make install'. In this
case, it will copy `foo' into the user's home directory. This is often
used by application make files, so that the application can be
installed in the correct directory when it has been correctly
compiled.
<p>
This is a slightly confusing subject to try and explain. If you don't
quite understand how make works, the best thing to do is to write a
simple program like ``hello world'' and a make file like the one above
and experiment. Then progress to using more than one source file, or
having the source file include a header file. (The `touch' command is
very useful here - it changes the date on a file without you having to
edit it).

<sect1><heading>FreeBSD Make Files</heading>
<p>
Make files can be rather complicated to write. Fortunately, BSD-based
systems like FreeBSD come with some very powerful ones as part of the
system.
<p>
One very good example of this is the FreeBSD ports system. Here's the
essential part of a typical ports Makefile:-

<code>
MASTER_SITES=   ftp://freefall.cdrom.com/pub/FreeBSD/LOCAL_PORTS/
DISTFILES=      scheme-microcode+dist-7.3-freebsd.tgz

.include <bsd.port.mk>
</code>

Now, if we go to the directory for this port and type make, the
following happens:-

<enum>

<item> A check is made to see if the source code for this port is
already on the system.

<item> If it isn't, an FTP connection to the URL in ``MASTER_SITES''
is set up to download the source.

<item> The checksum for the source is calculated and compared it with
one for a known, good, copy of the source. This is to make sure that
the source was not corrupted while in transit.

<item> Any changes required to make the source work on FreeBSD are
applied - this is known as ``patching''.

<item> Any special configuration needed for the source is done. (Many
Unix program distributions try to work out which version of Unix they
are being compiled on and which optional Unix features are present -
this is where they are given the information in the FreeBSD ports
scenario).

<item> The source code for the program is compiled. In effect, we
change to the directory where the source was unpacked and do 'make' -
the program's own make file has the necessary information to build the
program.

<item> We now have a compiled version of the program. If we wish, we
can test it now; when we feel confident about the program, we can type
'make install'. This will cause the program and any supporting files
it needs to be copied into the correct location; an entry is also made
into a ``package database'', so that the port can easily be
uninstalled later if we change our mind about it.

</enum>

Now I think you'll agree that's rather impressive for a four line
script!
<p>
The secret lies in the last line, which tells make to look in the
system make file called `bsd.port.mk'. It's easy to overlook this
line, but this is where all the clever stuff comes from - someone has
written a make file that tells make to do all the things above (plus a
couple of other things I didn't mention, not to mention handling any
errors that may occur) and anyone can get access to that just by
putting a single line in their own make file!
<p>
If you want to have a look at these system make files, they're in
/usr/share/mk, but it's probably best to wait until you've had a bit
of practice with make files, as they are very complicated (and if you
do look at them, make sure you have a flask of strong coffee handy!)

<sect1><heading>More advanced uses of make</heading>
<p>
Make is a very powerful tool, and can do much more than the simple
example above shows. Unfortunately, there are several different
versions of make, and they all differ considerably. The best way to
learn what they can do is probably to read the documentation -
hopefully this introduction will have given you a base from which you
can do this.
<p>
The version of make that comes with FreeBSD is the Berkeley make;
there is a tutorial for it in /usr/share/doc/psd/12.make. To view it,
do 

<tscreen><verb>
       zmore paper.ascii.gz
</verb></tscreen>

in that directory.
<p>
Many applications in the ports use GNU make, which has a very good set
of `info' pages. If you have installed any of these ports, GNU make
will automatically have been installed as `gmake'. It's also available
as a port and package in it's own right.
<p>
To view the info pages for GNU make, you will have to edit the `dir'
file in the /usr/local/info directory to add an entry for it. This
involves adding a line like

<tscreen><verb>
       * Make: (make).                 The GNU Make utility.
 </verb></tscreen>

to the file. Once you have done this, you can type `info' and then
select make from the menu (or in Emacs, do C-h i).

<sect><heading>Debugging</heading>
<p>
<sect1><heading>The Debugger</heading>
<p>
The debugger that comes with FreeBSD is called `gdb' (GNU debugger). You
start it up by typing 

<tscreen><verb> 
       gdb <progname>
</verb></tscreen>

although most people prefer to run it inside Emacs. You can do this by

<tscreen><verb>
       M-x gdb RET <progname> RET.
</verb></tscreen>

Using a debugger allows you to run the program under more controlled
circumstances. Typically, you can step through the program a line at a
time, inspect the value of variables, change them, tell the debugger to run
up to a certain point and then stop, and so on. You can even attach to a
program that's already running, or load a core file to investigate why the
program crashed.
<p>
It's even possible to debug the kernel, though that's a little trickier
than the user applications we'll be discussing in this section.
<p>
gdb has quite good on-line help, as well as a set of info pages, so this
section will concentrate on a few of the basic commands.
<p>
Finally, if you find its text-based command-prompt style off-putting,
there's a graphical front-end for it <htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/ports/devel/xxgdb.tgz"
name="xxgdb"> in the ports.
<p>
This section is intended to be an introduction to using gdb and does
not cover specialised topics such as debugging the kernel.

<sect1><heading>Running a program in the debugger</heading>
<p>
You'll need to have compiled the program with the `-g' option to get the
most out of using gdb. It will work without, but you'll only see the name
of the function you're in, instead of the source code. If you see a line
like 

<tscreen><verb>
       ...(no debugging symbols found)...
</verb></tscreen>

when gdb starts up, you'll know that the program wasn't compiled with
the `-g' option.
<p>
At the gdb prompt, type `break main'. This will tell the debugger to
skip over the preliminary set-up code in the program and start at the
beginning of your code. Now type `run' to start the program - it will
start at the beginning of the set-up code and then get stopped by the
debugger when it calls main(). (If you've ever wondered where main()
gets called from, now you know!).
<p>
You can now step through the program, a line at a time, by pressing
`n'.  If you get to a function call, you can step into it by pressing
`s'. Once you're in a function call, you can return from stepping into
a function call by pressing `f'. You can also use `up' and `down' to
take a quick look at the caller.
<p>
Here's a simple example of how to spot a mistake in a program with
gdb. This is our program (with a deliberate mistake):-

<code>
#include <stdio.h>

int bazz(int anint);

main() {
	int i;

	printf("This is my program\n");
	bazz(i);
	return 0;
}

int bazz(int anint) {
	printf("You gave me %d\n", anint);
	return anint;
}
</code>

This program sets i to be 5 and passes it to a function bazz() which prints
out the number we gave it.
<p>
When we compile and run the program we get

<tscreen><verb>
       cc -g -o temp temp.c
       ./temp
       This is my program
       anint = 4231
</verb></tscreen>

That wasn't what we expected! Time to see what's going on!

<tscreen><verb>
Current directory is ~/tmp/
GDB is free software and you are welcome to distribute copies of it
 under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for details.
GDB 4.13 (i386-unknown-freebsd), 
Copyright 1994 Free Software Foundation, Inc...
(gdb) break main				# Skip the set-up code
Breakpoint 1 at 0x160f: file temp.c, line 9.	# gdb puts breakpoint at main()
(gdb) run					# Run as far as main()
Starting program: /home/james/tmp/temp		# Program starts running 

Breakpoint 1, main () at temp.c:9		# gdb stops at main()
(gdb) n						# Go to next line
This is my program				# Program prints out "This .."
(gdb) s						# step into bazz()
bazz (anint=4231) at temp.c:17			# gdb displays stack frame
</verb></tscreen>

Hang on a minute! How did anint get to be 4231? Didn't we set it to be 5
in main()? Let's move up to main() and have a look.

<tscreen><verb>
(gdb) up					# Move up call stack
#1  0x1625 in main () at temp.c:11		# gdb displays stack frame
(gdb) p i					# Show us the value of i
$1 = 4231					# gdb displays 4231
</verb></tscreen>

Oh dear! Looking at the code, we forgot to initialise i. We meant to put

<code>
...
main() {
	int i;

	i = 5;
	printf("This is my program\n");
...
</code>

but we missed the `i=5;' line out.  As we didn't initialise i, it had
whatever number happened to be in that area of memory when the program
ran, which in this case happened to be 4231.
<p>
Note that gdb displays the stack frame every time we go into or out of
a function, even if we're using `up' and `down' to move around the
call stack.  This shows the name of the function and the values of its
arguments, which helps us keep track of where we are and what's going
on. (The stack is a storage area where the program stores information
about the arguments passed to functions and where to go when it
returns from a function call).

<sect1><heading>Examining a core file</heading>
<p>
A core file is basically a file which contains the complete state of
the process when it crashed. In ``the good old days'', programmers had
to print out hex listings of core files and sweat over machine code
manuals, but now life is a bit easier. Incidentally, under FreeBSD and
other 4.4BSD systems, a core file is called ``progname.core'' instead
of just core, to make it clearer which program a core file belongs to.
<p>
To examine a core file, start up gdb in the usual way. Instead of
typing `break' or `run', type

<tscreen><verb>
       core progname.core 
</verb></tscreen>

(if you're not in the same directory as the core file, you'll have to
do `dir /path/to/core/file' first).
<p>
You should see something like this:-

<tscreen><verb>
Current directory is ~/tmp/
GDB is free software and you are welcome to distribute copies of it
 under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for details.
GDB 4.13 (i386-unknown-freebsd), 
Copyright 1994 Free Software Foundation, Inc...
(gdb) core a.out.core
Core was generated by `a.out'.
Program terminated with signal 11, Segmentation fault.
Cannot access memory at address 0x7020796d.
#0  0x164a in foobar (some_arg=0x5) at temp.c:17
</verb></tscreen>

In this case, the program was called `a.out', so the core file is
called `a.out.core'. We can see that the program crashed due to trying
to access an area in memory that was not available to it in a function
called `bazz'.
<p>
Sometimes it's useful to be able to see how a function was called, as
the problem could have occurred a long way up the call stack in a
complex program. The `bt' command causes gdb to print out a back-trace
of the call stack:-

<tscreen><verb>
(gdb) bt
#0  0x164a in bazz (anint=0x5) at temp.c:17
#1  0xefbfd888 in end ()
#2  0x162c in main () at temp.c:11
</verb></tscreen>

The end() function is called when a program crashes; in this case, the
bazz() function was called from main().

<sect1><heading>Attaching to a running program</heading>
<p>
One of the neatest features about gdb is that it can attach to a
program that's already running. (Of course, that assumes you have
sufficient permissions to do so). A common problem is when you are
stepping through a program that forks, and you want to trace the
child, but the debugger will only let you trace the parent.
<p>
What you do is start up another gdb, use `ps' to find the process ID
for the child, and do

<tscreen><verb>
       attach <pid>
</verb></tscreen>

in gdb, and then debug as usual.
<p>
``That's all very well,'' you're probably thinking, ``but by the time
I've done that, the child process will be over the hill and far
away''. Fear not, gentle reader, here's how to do it (courtesy of the
gdb info pages):-

<tscreen><verb>
...
if ((pid = fork()) < 0)		/* _Always_ check this */
	error();
else if (pid == 0) {		/* child */
	int PauseMode = 1;

	while (PauseMode)
		sleep(10);	/* Wait until someone attaches to us */
	...
} else {			/* parent */
	...
</verb></tscreen>

Now all you have to do is attach to the child, set PauseMode to 0, and
wait for the sleep() call to return!

<sect><heading>Using Emacs as a Development Environment</heading>
<p>
<sect1><heading>Emacs</heading>
<p>
Unfortunately, Unix systems don't come with the kind of
everything-you-ever-wanted-and-lots-more-you-didn't-in-one-gigantic-package
integrated development environments that other systems have (at least,
not unless you pay out very large sums of money). However, it is
possible to set up your own environment. It may not be as pretty, and
it may not be quite as integrated, but you can set it up the way you
want it. And it's free. And you have the source to it.
<p>
The key to it all is Emacs. Now there are some people who loathe it,
but many who love it. If you're one of the former, I'm afraid this
section will hold little of interest to you. Also, you'll need a fair
amount of memory to run it - I'd recommend 8MB in text mode and 16MB
in X as the bare minimum to get reasonable performance.
<p>
Emacs is basically a highly customisable editor - indeed, it has been
customised to the point where it's more like an operating system than
an editor! (Many developers and sysadmins do in fact spend practically
all their time working inside Emacs, leaving it only to log out).
<p>
It's impossible even to summarise everything Emacs can do here, but
here are some of the features of interest to developers:-

<itemize>
<item> Very powerful editor, allowing search-and-replace on both
  strings and regular expressions (patterns), jumping to start/end of
  block expression, etc, etc.

<item> Pull-down menus and online help.

<item> Language-dependent syntax highlighting and indentation.

<item> Completely customisable.

<item> You can compile and debug programs within Emacs.

<item> On a compilation error, you can jump to the offending line of source
  code.

<item> Friendly-ish front-end to the `info' program used for reading GNU
  hypertext documentation (including the documentation on Emacs).

<item> Friendly front-end to GDB, allowing you to look at the source code
  as you step through your program.

<item> You can read Usenet news and mail while your program is compiling ;-)
</itemize>

And doubtless many more that I've overlooked.
<p>
Emacs can be installed on FreeBSD using <htmlurl
url="ftp://ftp.freebsd.org:pub/FreeBSD/packages/editors/emacs"
name="the Emacs package">.
<p>
Once it's installed, start it up and do C-h t to read an Emacs
tutorial - that means hold down the control key, press `h', let go of
the control key, and then press t. (Alternatively, you can you use
the mouse to select ``Emacs Tutorial'' from the ``Help'' menu).
<p>
Although Emacs does have menus, it's well worth learning the key
bindings, as it's much quicker when you're editing something to press
a couple of keys than to try and find the mouse and then click on the
right place. And, when you're talking to seasoned Emacs users, you'll
find they often casually throw around expressions like

<tscreen><verb>
       M-x replace-s RET foo RET bar RET
</verb></tscreen>

so it's useful to know what they mean. And in any case, Emacs has far
too many useful functions for them to all fit on the menu bars.
<p>
Fortunately, it's quite easy to pick up the key-bindings, as they're
displayed next to the menu item. (My advice is to use the menu item
for, say, opening a file until you understand how it works and feel
confident with it, then try doing C-x C-f. When you're happy with
that, move on to another menu command). 
<p>
If you can't remember what a particular combination of keys does,
select ``Describe Key'' from the ``Help'' menu and type it in - Emacs
will tell you what it does. You can also use the ``Command Apropos''
menu item to find out all the commands which contain a particular word
in them, with the key binding next to it.
<p>
By the way, the expression above means hold down the Meta key, press
`x', release the Meta key, type replace-s (short for ``replace-string''
- another feature of Emacs is that you can abbreviate commands), press
the return key, type foo (the string you want replaced), press the
return key, type bar (the string you want to replace ``foo'' with) and
press return again. Emacs will then do the search-and-replace
operation you've just requested.
<p>
If you're wondering what on earth the Meta key is, it's a special key
that many Unix workstations have. Unfortunately, PC's don't have one,
so it's usually the ``alt'' key (or if you're unlucky, the ``escape''
key).
<p>
Oh, and to get out of Emacs, do C-c C-x (that means hold down the
control key, press `c', press `x' and release the control key). If you
have any unsaved files open, Emacs will ask you if you want to save
them. (Ignore the bit in the documentation where it says C-z is the
usual way to leave Emacs - that leaves Emacs hanging around in the
background, and is only really useful if you're on a system which
doesn't have virtual terminals).

<sect1><heading>Configuring Emacs</heading>
<p>
Emacs does many wonderful things, some of them are built in, some of
them need to be configured.
<p>
Instead of using a proprietary macro language for configuration, Emacs
uses a version of Lisp specially adapted for editors, known as Emacs
Lisp. This can be quite useful if you want to go on and learn
something like Common Lisp, as it's considerably smaller than Common
Lisp (although still quite big!).
<p>
The best way to learn Emacs Lisp is to download the <htmlurl
url="ftp://prep.ai.mit.edu:pub/gnu/elisp-manual-19-2.4.tar.gz"
name="Emacs Tutorial">
<p>
However, there's no need to actually know any Lisp to get started with
configuring Emacs, as I've included a sample ``.emacs'' file, which
should be enough to get you started. Just copy it into your home
directory and restart Emacs if it's already running; it will read the
commands from the file and (hopefully) give you a useful basic setup.

<sect1><heading>A sample .emacs file</heading>
<p>
Unfortunately, there's far too much here to explain it in detail;
however there are one or two points worth mentioning.

<itemize>
<item> Everything beginning with a `;' is a comment and is ignored by Emacs.

<item> In the first line, the -*- Emacs-Lisp -*- is so that we can edit
the .emacs file itself within Emacs and get all the fancy features for
editing Emacs Lisp (Emacs usually tries to guess this based on the
filename, and may not get it right for .emacs).

<item> The `tab' key is bound to an indentation function in some modes, so
when you press the tab key, it will indent the current line of
code. If you want to put a tab character in whatever you're writing,
hold the control key down while you're pressing the tab key.

<item> This file supports syntax highlighting for C, C++, Perl, Lisp and
Scheme (by guessing the language from the filename).

<item> Emacs already has a pre-defined function called ``next-error''.
In a compilation output window, this allows you to move from one
compilation error to the next by doing M-n; we define a complementary
function, ``previous-error'', that allows you to go to a previous
error by doing M-p. The nicest feature of all is that C-c C-c will
open up the source file in which the error occurred and jump to the
appropriate line.

<item> We enable Emacs's ability to act as a server, so that if you're doing
something outside Emacs and you want to edit a file, you can just
type in 
<tscreen><verb>
       emacsclient <filename>
</verb></tscreen>

and then you can edit the file in your Emacs! (Many Emacs users set
their EDITOR environment to `emacsclient' so this happens every time
they need to edit a file).
</itemize>

<tscreen><verb>
;; -*-Emacs-Lisp-*-

;; This file is designed to be re-evaled; use the variable first-time
;; to avoid any problems with this.
(defvar first-time t 
  "Flag signifying this is the first time that .emacs has been evaled")

;; Meta
(global-set-key "\M- " 'set-mark-command)
(global-set-key "\M-\C-h" 'backward-kill-word)
(global-set-key "\M-\C-r" 'query-replace)
(global-set-key "\M-r" 'replace-string)
(global-set-key "\M-g" 'goto-line)
(global-set-key "\M-h" 'help-command)

;; Function keys
(global-set-key [f1] 'manual-entry)
(global-set-key [f2] 'info)
(global-set-key [f3] 'repeat-complex-command)
(global-set-key [f4] 'advertised-undo)
(global-set-key [f5] 'eval-current-buffer)
(global-set-key [f6] 'buffer-menu)
(global-set-key [f7] 'other-window)
(global-set-key [f8] 'find-file)
(global-set-key [f9] 'save-buffer)
(global-set-key [f10] 'next-error)
(global-set-key [f11] 'compile)
(global-set-key [f12] 'grep)
(global-set-key [C-f1] 'compile)
(global-set-key [C-f2] 'grep)
(global-set-key [C-f3] 'next-error)
(global-set-key [C-f4] 'previous-error)
(global-set-key [C-f5] 'display-faces)
(global-set-key [C-f8] 'dired)
(global-set-key [C-f10] 'kill-compilation)

;; Keypad bindings
(global-set-key [up] "\C-p")
(global-set-key [down] "\C-n")
(global-set-key [left] "\C-b")
(global-set-key [right] "\C-f")
(global-set-key [home] "\C-a")
(global-set-key [end] "\C-e")
(global-set-key [prior] "\M-v")
(global-set-key [next] "\C-v")
(global-set-key [C-up] "\M-\C-b")
(global-set-key [C-down] "\M-\C-f")
(global-set-key [C-left] "\M-b")
(global-set-key [C-right] "\M-f")
(global-set-key [C-home] "\M-<")
(global-set-key [C-end] "\M->")
(global-set-key [C-prior] "\M-<")
(global-set-key [C-next] "\M->")

;; Mouse
(global-set-key [mouse-3] 'imenu)

;; Misc
(global-set-key [C-tab] "\C-q\t")	; Control tab quotes a tab.
(setq backup-by-copying-when-mismatch t)

;; Treat 'y' or <CR> as yes, 'n' as no.
(fset 'yes-or-no-p 'y-or-n-p)
    (define-key query-replace-map [return] 'act)
    (define-key query-replace-map [?\C-m] 'act)

;; Load packages
(require 'desktop)
(require 'tar-mode)

;; Pretty diff mode
(autoload 'ediff-buffers "ediff" "Intelligent Emacs interface to diff" t)
(autoload 'ediff-files "ediff" "Intelligent Emacs interface to diff" t)
(autoload 'ediff-files-remote "ediff"
  "Intelligent Emacs interface to diff") 
</verb></tscreen>
<tscreen><verb>
(if first-time
    (setq auto-mode-alist
	  (append '(("\\.cpp$" . c++-mode)
		    ("\\.hpp$" . c++-mode)
                    ("\\.lsp$" . lisp-mode)
		    ("\\.scm$" . scheme-mode)
		    ("\\.pl$" . perl-mode)
		    ) auto-mode-alist)))

;; Auto font lock mode
(defvar font-lock-auto-mode-list 
  (list 'c-mode 'c++-mode 'c++-c-mode 'emacs-lisp-mode 'lisp-mode 'perl-mode 'scheme-mode)
  "List of modes to always start in font-lock-mode")

(defvar font-lock-mode-keyword-alist
  '((c++-c-mode . c-font-lock-keywords)
    (perl-mode . perl-font-lock-keywords))
  "Associations between modes and keywords")

(defun font-lock-auto-mode-select ()
  "Automatically select font-lock-mode if the current major mode is
in font-lock-auto-mode-list"
  (if (memq major-mode font-lock-auto-mode-list) 
      (progn
	(font-lock-mode t))
    )
  )

(global-set-key [M-f1] 'font-lock-fontify-buffer)

;; New dabbrev stuff
;(require 'new-dabbrev)
(setq dabbrev-always-check-other-buffers t)
(setq dabbrev-abbrev-char-regexp "\\sw\\|\\s_")
(add-hook 'emacs-lisp-mode-hook
	  '(lambda () 
	     (set (make-local-variable 'dabbrev-case-fold-search) nil)
	     (set (make-local-variable 'dabbrev-case-replace) nil)))
(add-hook 'c-mode-hook
	  '(lambda () 
	     (set (make-local-variable 'dabbrev-case-fold-search) nil)
	     (set (make-local-variable 'dabbrev-case-replace) nil)))
(add-hook 'text-mode-hook
	  '(lambda () 
	     (set (make-local-variable 'dabbrev-case-fold-search) t)
	     (set (make-local-variable 'dabbrev-case-replace) t)))

;; C++ and C mode...
(defun my-c++-mode-hook ()
  (setq tab-width 4)
  (define-key c++-mode-map "\C-m" 'reindent-then-newline-and-indent)
  (define-key c++-mode-map "\C-ce" 'c-comment-edit)
  (setq c++-auto-hungry-initial-state 'none)
  (setq c++-delete-function 'backward-delete-char)
  (setq c++-tab-always-indent t)
  (setq c-indent-level 4)
  (setq c-continued-statement-offset 4)
  (setq c++-empty-arglist-indent 4))

(defun my-c-mode-hook ()
  (setq tab-width 4)
  (define-key c-mode-map "\C-m" 'reindent-then-newline-and-indent)
  (define-key c-mode-map "\C-ce" 'c-comment-edit)
  (setq c-auto-hungry-initial-state 'none)
  (setq c-delete-function 'backward-delete-char)
  (setq c-tab-always-indent t)
;; BSD-ish indentation style
  (setq c-indent-level 4)
  (setq c-continued-statement-offset 4)
  (setq c-brace-offset -4)
  (setq c-argdecl-indent 0)
  (setq c-label-offset -4))

;; Perl mode
(defun my-perl-mode-hook ()
  (setq tab-width 4)
  (define-key c++-mode-map "\C-m" 'reindent-then-newline-and-indent)
  (setq perl-indent-level 4)
  (setq perl-continued-statement-offset 4))

;; Scheme mode...
(defun my-scheme-mode-hook ()
  (define-key scheme-mode-map "\C-m" 'reindent-then-newline-and-indent))

;; Emacs-Lisp mode...
(defun my-lisp-mode-hook ()
  (define-key lisp-mode-map "\C-m" 'reindent-then-newline-and-indent)
  (define-key lisp-mode-map "\C-i" 'lisp-indent-line)
  (define-key lisp-mode-map "\C-j" 'eval-print-last-sexp))

;; Add all of the hooks...
(add-hook 'c++-mode-hook 'my-c++-mode-hook)
(add-hook 'c-mode-hook 'my-c-mode-hook)
(add-hook 'scheme-mode-hook 'my-scheme-mode-hook)
(add-hook 'emacs-lisp-mode-hook 'my-lisp-mode-hook)
(add-hook 'lisp-mode-hook 'my-lisp-mode-hook)
(add-hook 'perl-mode-hook 'my-perl-mode-hook)

;; Complement to next-error
(defun previous-error (n)
  "Visit previous compilation error message and corresponding source code."
  (interactive "p")
  (next-error (- n)))
</verb></tscreen>
<tscreen><verb>
;; Misc...
(transient-mark-mode 1)
(setq mark-even-if-inactive t)
(setq visible-bell nil)
(setq next-line-add-newlines nil)
(setq compile-command "make")
(setq suggest-key-bindings nil)
(put 'eval-expression 'disabled nil)
(put 'narrow-to-region 'disabled nil)
(put 'set-goal-column 'disabled nil)

;; Elisp archive searching
(autoload 'format-lisp-code-directory "lispdir" nil t)
(autoload 'lisp-dir-apropos "lispdir" nil t)
(autoload 'lisp-dir-retrieve "lispdir" nil t)
(autoload 'lisp-dir-verify "lispdir" nil t)

;; Font lock mode
(defun my-make-face (face colour &amp;optional bold)
  "Create a face from a colour and optionally make it bold"
  (make-face face)
  (copy-face 'default face)
  (set-face-foreground face colour)
  (if bold (make-face-bold face))
  )

(if (eq window-system 'x)
    (progn
      (my-make-face 'blue "blue")
      (my-make-face 'red "red")
      (my-make-face 'green "dark green")
      (setq font-lock-comment-face 'blue)
      (setq font-lock-string-face 'bold)
      (setq font-lock-type-face 'bold)
      (setq font-lock-keyword-face 'bold)
      (setq font-lock-function-name-face 'red)
      (setq font-lock-doc-string-face 'green)
      (add-hook 'find-file-hooks 'font-lock-auto-mode-select)

      (setq baud-rate 1000000)
      (global-set-key "\C-cmm" 'menu-bar-mode)
      (global-set-key "\C-cms" 'scroll-bar-mode)
      (global-set-key [backspace] 'backward-delete-char)
					;      (global-set-key [delete] 'delete-char)
      (standard-display-european t)
      (load-library "iso-transl")))

;; X11 or PC using direct screen writes
(if window-system
    (progn
      ;;      (global-set-key [M-f1] 'hilit-repaint-command)
      ;;      (global-set-key [M-f2] [?\C-u M-f1])
      (setq hilit-mode-enable-list  
	    '(not text-mode c-mode c++-mode emacs-lisp-mode lisp-mode
		  scheme-mode)
	    hilit-auto-highlight nil
	    hilit-auto-rehighlight 'visible
	    hilit-inhibit-hooks nil
	    hilit-inhibit-rebinding t)
      (require 'hilit19)
      (require 'paren))
  (setq baud-rate 2400)			; For slow serial connections
  )

;; TTY type terminal
(if (and (not window-system) 
	 (not (equal system-type 'ms-dos)))
    (progn
      (if first-time
	  (progn
	    (keyboard-translate ?\C-h ?\C-?)
	    (keyboard-translate ?\C-? ?\C-h)))))

;; Under UNIX
(if (not (equal system-type 'ms-dos))
    (progn
      (if first-time
	  (server-start))))

;; Add any face changes here
(add-hook 'term-setup-hook 'my-term-setup-hook)
(defun my-term-setup-hook ()
  (if (eq window-system 'pc)
      (progn
;;	(set-face-background 'default "red")
	)))

;; Restore the "desktop" - do this as late as possible
(if first-time
    (progn
      (desktop-load-default)
      (desktop-read)))

;; Indicate that this file has been read at least once
(setq first-time nil)

;; No need to debug anything now
(setq debug-on-error nil)

;; All done
(message "All done, %s%s" (user-login-name) ".")

</verb></tscreen>

<sect1><heading>Extending the Range of Languages Emacs Understands</heading>
<p>
Now, this is all very well if you only want to program in the
languages already catered for in the .emacs file (C, C++, Perl, Lisp
and Scheme), but what happens if a new language called "whizbang"
comes out, full of exciting features?
<p>
The first thing to do is find out if "whizbang" comes with any files
that tell Emacs about the language. These usually end in ".el", short
for "Emacs Lisp". For example, if "whizbang" is a FreeBSD port, we can
locate these files by doing

<tscreen><verb> 
       find /usr/ports/lang/whizbang -name *.el -print
</verb></tscreen>

and install them by copying them into Emac's site Lisp directory. On
FreeBSD 2.1.0-RELEASE, this is /usr/local/share/emacs/site-lisp.

So for example, if the output from the find command was 

<tscreen><verb>
       /usr/ports/lang/whizbang/work/misc/whizbang.el
</verb></tscreen>

we would do 

<tscreen><verb>
       cp /usr/ports/lang/whizbang/work/misc/whizbang.el /usr/local/share/emacs/site-lisp
</verb></tscreen>

Next, we need to decide what extension whizbang source files
have. Let's say for the sake of argument that they all end in
`.wiz'. We need to add an entry to our .emacs file to make sure Emacs
will be able to use the information in whizbang.el.
<p>
Find the auto-mode-alist entry in .emacs and add a line for whizbang,
such as:-

<tscreen><verb>
		...
                    ("\\.lsp$" . lisp-mode)
                    ("\\.wiz$" . whizbang-mode)
		    ("\\.scm$" . scheme-mode)
		...
</verb></tscreen>

This means that Emacs will automatically go into whizbang-mode when
you edit a file ending in .wiz.
<p>
Just below this, you'll find the font-lock-auto-mode-list entry. Add
whizbang-mode to it like so:-

<tscreen><verb>
;; Auto font lock mode
(defvar font-lock-auto-mode-list 
  (list 'c-mode 'c++-mode 'c++-c-mode 'emacs-lisp-mode 'whizbang-mode 'lisp-mode 'perl-mode 'scheme-mode)
  "List of modes to always start in font-lock-mode")
</verb></tscreen>

This means that Emacs will always enable font-lock-mode (ie syntax
highlighting) when editing a .wiz file.
<p>
And that's all that's needed. If there's anything else you want done
automatically when you open up a .wiz file, you can add a
whizbang-mode hook (see my-scheme-mode-hook for a simple example that
adds auto-indent).

<sect><heading>Further Reading</heading>
<sect1><heading>Bibliography</heading>
<p>
<itemize>
<item>
Brian Harvey and Matthew Wright
<em>Simply Scheme</em>
MIT 1994.
<newline>ISBN 0-262-08226-8
</item>

<item>
Randall Schwartz
<em>Learning Perl</em>
O'Reilly 1993
<newline>ISBN 1-56592-042-2
</item>

<item>
Patrick Henry Winston and Berthold Klaus Paul Horn
<em>Lisp (3rd Edition)</em>
Addison-Wesley 1989
<newline>ISBN 0-201-08319-1
</item>

<item>
Brian W. Kernighan and Rob Pike
<em>The Unix Programming Environment</em>
Prentice-Hall 1984
<newline>ISBN 0-13-937681-X
</item>

<item>
Brian W. Kernighan and Dennis M. Ritchie
<em>The C Programming Language (2nd Edition)</em>
Prentice-Hall 1988
<newline>ISBN 0-13-110362-8
</item>

<item>
Bjarne Stroustrup
<em>The C++ Programming Language</em>
Addison-Wesley 1991
<newline>ISBN 0-201-53992-6
</item>

<item>
W. Richard Stevens
<em>Advanced Programming in the Unix Environment</em>
Addison-Wesley 1992
<newline>ISBN 0-201-56317-7
</item>

<item>
W. Richard Stevens
<em>Unix Network Programming</em>
Prentice-Hall 1990
<newline>ISBN 0-13-949876-1
</item>
</itemize>
</article>