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<!-- $Id: article.sgml,v 1.5 1999-03-21 16:16:17 wosch Exp $ -->
<!-- The FreeBSD Documentation Project -->

<!DOCTYPE BOOK PUBLIC "-//Davenport//DTD DocBook V3.0//EN">
<book>
<bookinfo>
<bookbiblio>
<title>A User's Guide to FreeBSD Programming Tools</title>

<authorgroup>
<author>
<firstname>James</firstname>
<surname>Raynard</surname>
<affiliation>
<address>
<email>jraynard@freebsd.org</email>
</address>
</affiliation>
</author></authorgroup>

<pubdate>August 17, 1997</pubdate>

<copyright>
<year>1997</year>
<holder>James Raynard</holder>
</copyright>

<abstract><para>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 <emphasis>not</emphasis> 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</para></abstract>
</bookbiblio>
</bookinfo>

<chapter>
<title>Introduction<anchor id=foo></title>
  
<para>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
<command>sed</> and <command>awk</>. If that is not enough, there are
many more compilers and interpreters in the Ports collection. FreeBSD
is very compatible with standards such as <acronym>POSIX</> and
<acronym>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.</para>

<para>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.</para>

<para>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!</para>
  
</chapter>

<chapter>
<title>Introduction to Programming</title>

<para>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 <quote>commands</quote> as they are usually
called. One way uses an <firstterm>interpreter</>, the other a
<firstterm>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.</para>


  
<sect1>
<title>Interpreters</title>

<para>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.</para>
  
<para>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.</para>

<para>In my opinion, interpreted languages are the best way to start
if you have not 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 (<command>sh</>,
<command>csh</>) is itself an interpreter, and many people do in fact
write shell <quote>scripts</quote> to help with various
<quote>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.</para>
  
</sect1>

<sect1>
<title>Interpreters available with FreeBSD</title>

<para>Here is a list of interpreters that are available as <ulink
URL="ftp://ftp.freebsd.org:pub/FreeBSD/packages/">FreeBSD
packages</ulink>, with a brief discussion of some of the more popular
interpreted languages. </para>

<para>To get one of these packages, all you need to do is to click on
the hotlink for the package, then run
<screen>$ <userinput>pkg_add <replaceable>package name</></userinput></screen>
</para>
  
<para>as root. Obviously, you will need to have a fully functional FreeBSD
2.1.0 or later system for the package to work!</para>
  
<para>
<variablelist>
<varlistentry><term><acronym>BASIC</></term>

<listitem><para>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, <acronym>BASIC</> has been the first programming language
for many programmers. It's also the foundation for <trademark>Visual
Basic</>.</para>

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

<varlistentry><term>Lisp</term>
<listitem><para>A language that was developed in the late 1950s as an alternative to
the <quote>number-crunching</quote> 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 <quote>List Processing</quote>. Very popular in AI
(Artificial Intelligence) circles.</para>
  
<para>Lisp is an extremely powerful and sophisticated language, but
can be rather large and unwieldy. </para>

<para>FreeBSD has <ulink
URL="ftp://ftp.freebsd.org:pub/FreeBSD/packages/gcl-2.0.tgz">GNU
Common Lisp</ulink> available as a package.</para>
  
</listitem>
</varlistentry>

<varlistentry><term>Perl</term>
<listitem><para>Very popular with system administrators for writing
scripts; also often used on World Wide Web servers for writing <acronym>CGI</>
scripts.</para>

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

</listitem>
</varlistentry>

<varlistentry><term>Scheme</term>
<listitem><para>A dialect of Lisp that is rather more compact and
cleaner than Common Lisp. Popular in Universities as it is 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.</para>

<para>FreeBSD has packages of the 
<ulink URL="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/elk-3.0.tgz">Elk Scheme Interpreter</ulink>, the 
<ulink URL="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/mit-scheme-7.3.tgz">MIT Scheme Interpreter</ulink> and the 
<ulink URL="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/scm-4e1.tgz">SCM Scheme Interpreter</ulink>.</para>
  
</listitem>
</varlistentry>

<varlistentry><term>Icon</term>
<listitem><para><ulink URL="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/icon-9.0.tgz">The Icon Programming Language</ulink>.</para>
</listitem>
</varlistentry>

<varlistentry><term>Logo</term>
<listitem><para><ulink URL="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/ucblogo-3.3.tgz">Brian Harvey's LOGO Interpreter</ulink>.</para>
</listitem>
</varlistentry>

<varlistentry><term>Python</term>
<listitem><para><ulink URL="ftp://ftp.freebsd.org:pub/FreeBSD/packages/lang/python-1.2">The Python Object-Oriented Programming Language</ulink></para>
</listitem>
</varlistentry>

</variablelist>
</para>
  
</sect1>

<sect1>
<title>Compilers</title>

<para>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 did not 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.<footnote><para>If you run it in
the shell, you may get a core dump.</para></footnote></para>

<para>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 closely with the operating system&mdash;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 would not be acceptable in an interpreter. And
distributing a program written for a compiler is usually more
straightforward than one written for an interpreter&mdash;you can just
give them a copy of the executable, assuming they have the same
operating system as you.</para>

<para>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.</para>
  
<para>As the edit-compile-run-debug cycle is rather tedious when
using separate programs, many commercial compiler makers have
produced Integrated Development Environments (<acronym>IDE</acronym>s
for short). FreeBSD does not have an <acronym>IDE</> as such; however
it is possible to use Emacs for this purpose. This is discussed in
<xref linkend="emacs">.</para>
  
</sect1>
</chapter>

<chapter>
<title>Compiling with <command>cc</command></title>

<para>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 <command>cc</> or <command>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.</para>

<para>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.</para>

<procedure>
<step><para>Pre-process your source code to remove comments and do other
tricks like expanding macros in C.
</para></step>

<step><para>Check the syntax of your code to see if you have obeyed the
rules of the language. If you have not, it will complain!
</para></step>

<step><para>Convert the source code into assembly
language&mdash;this is very close to machine code, but still
understandable by humans. Allegedly.<footnote><para>To be strictly
accurate, <command>cc</> converts the source code into its own,
machine-independent <firstterm>p-code</> instead of assembly language
at this stage.</para></footnote></para></step>

<step><para>Convert the assembly language into machine
code&mdash;yep, we are talking bits and bytes, ones and zeros
here.</para></step>

<step><para>Check that you have used things like functions and global
variables in a consistent way. For example, if you have called a
non-existent function, it will complain.</para></step>

<step><para>If you are trying to produce an executable from several
source code files, work out how to fit them all together.</para></step>

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

<step><para>Finally, write the executable on the file
system.</para></step>

</procedure>
  
<para>The word <firstterm>compiling</> is often used to refer to just
steps 1 to 4&mdash;the others are referred to as
<firstterm>linking</>. Sometimes step 1 is referred to as
<firstterm>pre-processing</> and steps 3-4 as
<firstterm>assembling</>.</para>

<para>Fortunately, almost all this detail is hidden from you, as
<command>cc</> is a front end that manages calling all these programs
with the right arguments for you; simply typing
<screen>$ <userinput>cc foobar.c</></screen></para>
  
<para>will cause <filename>foobar.c</> to be compiled by all the
steps above. If you have more than one file to compile, just do
something like
<screen>$ <userinput>cc foo.c bar.c</></screen>
</para>
  
<para>Note that the syntax checking is just that&mdash;checking the
syntax. It will not 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.<footnote><para>In case you
didn't know, a binary sort is an efficient way of sorting things into
order and a bubble sort isn't.</para></footnote></para>

<para>There are lots and lots of options for <command>cc</>, which
are all in the man page.  Here are a few of the most important ones,
with examples of how to use them.</para>

<variablelist>
<varlistentry><term><option>-o <replaceable>filename</replaceable></></term>

<listitem><para>The output name of the file. If you do not use this
option, <command>cc</> will  produce an executable called
<filename>a.out</>.<footnote><para>The reasons for this are buried in
the mists of history.</para></footnote></para>

<informalexample>
<screen>$ <userinput>cc foobar.c</>               <lineannotation>executable is <filename>a.out</></>
$ <userinput>cc -o foobar foobar.c</>     <lineannotation>executable is <filename>foobar</></></screen>
</informalexample>
</listitem>
</varlistentry>

<varlistentry><term><option>-c</option></term>
<listitem><para>Just compile the file, do not link it. Useful for toy
programs where you just want to check the syntax, or if you are using
a <filename>Makefile</filename>.</para>

<informalexample>
<screen>$ <userinput>cc -c foobar.c</userinput></screen>
</informalexample>
  
<para>This will produce an <firstterm>object file</> (not an
executable) called <filename>foobar.o</filename>. This can be linked
together with other object files into an executable.</para>

</listitem>
</varlistentry>

<varlistentry><term><option>-g</option></term>

<listitem><para>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 <emphasis>very</emphasis> useful; the disadvantage
is that all this extra information makes the program much bigger.
Normally, you compile with <option>-g</option> while you are
developing a program and then compile a <quote>release
version</quote> without <option>-g</option> when you're satisfied it
works properly.</para>

<informalexample>
<screen>$ <userinput>cc -g foobar.c</userinput></screen>
</informalexample>
  
<para>This will produce a debug version of the
program.<footnote><para>Note, we didn't use the <option>-o</option>
flag to specify the executable name, so we will get an executable
called <filename>a.out</filename>. Producing a debug version called
<filename>foobar</filename> is left as an exercise for the
reader!</para></footnote></para>

</listitem>
</varlistentry>

<varlistentry><term><option>-O</option></term>

<listitem><para>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 <option>-O</option> to specify a higher level of optimisation,
but this often exposes bugs in the compiler's optimiser. For
instance, the version of <command>cc</command> that comes with the
2.1.0 release of FreeBSD is known to produce bad code with the
<option>-O2</option> option in some circumstances.</para>

<para>Optimisation is usually only turned on when compiling a release
version.</para>

<informalexample>
<screen>$ <userinput>cc -O -o foobar foobar.c</userinput></screen>
</informalexample>
  
<para>This will produce an optimised version of
<filename>foobar</filename>.</para>

</listitem>
</varlistentry>
</variablelist>

<para>The following three flags will force <command>cc</command> to
check that your code complies to the relevant international standard,
often referred to as the <acronym>ANSI</acronym> standard, though
strictly speaking it is an <acronym>ISO</acronym> standard.</para>

<variablelist>

<varlistentry><term><option>-Wall</option></term>

<listitem><para>Enable all the warnings which the authors of
<command>cc</command> believe are worthwhile. Despite the name, it
will not enable all the warnings <command>cc</command> is capable
of.</para></listitem>

</varlistentry>

<varlistentry><term><option>-ansi</option></term>

<listitem>
<para>Turn off most, but not all, of the non-<acronym>ANSI</>&nbsp;C
features provided by <command>cc</command>. Despite the name, it does
not guarantee strictly that your code will comply to the
standard.</para>
</listitem>

</varlistentry>

<varlistentry><term><option>-pedantic</option></term>

<listitem>
<para>Turn off <emphasis>all</emphasis>
<command>cc</command>'s non-<acronym>ANSI</>&nbsp;C features.</para>
</listitem>

</varlistentry>
</variablelist>

<para>Without these flags, <command>cc</command> 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&mdash;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 <firstterm>portable code</firstterm>.</para>

<para>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&mdash;and who knows
what you may be using in a few years time?</para>
  
<informalexample>
<screen>$ <userinput>cc -Wall -ansi -pedantic -o foobar foobar.c</userinput></screen>
</informalexample>

<para>This will produce an executable <filename>foobar</filename>
after checking <filename>foobar.c</filename> for standard
compliance.</para>
  
<variablelist>

<varlistentry><term><option>-l<replaceable>library</replaceable></option></term>

<listitem><para>Specify a function library to be used during when
linking.</para>

<para>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.</para>
  
<para>The rule is that if the library is called
<filename>lib<replaceable>something</replaceable>.a</filename>, you
give <command>cc</command> the argument
<option>-l<replaceable>something</replaceable></option>. For example,
the math library is <filename>libm.a</filename>, so you give
<command>cc</command> the argument <option>-lm</option>. A common
<quote>gotcha</quote> with the math library is that it has to be the
last library on the command line.</para>

<informalexample>
<screen>$ <userinput>cc -o foobar foobar.c -lm</userinput></screen>
</informalexample>

<para>This will link the math library functions into
<filename>foobar</filename>.</para>

<para>If you are compiling C++ code, you need to add
<option>-lg++</option>, or <option>-lstdc++</option> if you are using
FreeBSD 2.2 or later, to the command line argument to link the C++
library functions. Alternatively, you can run <command>c++</command>
instead of <command>cc</command>, which does this for you.
<command>c++</command> can also be invoked as <command>g++</command>
on FreeBSD.</para>

<informalexample>
<screen>$ <userinput>cc -o foobar foobar.cc -lg++</userinput>     <lineannotation>For FreeBSD 2.1.6 and earlier</>
$ <userinput>cc -o foobar foobar.cc -lstdc++</userinput>  <lineannotation>For FreeBSD 2.2 and later</>
$ <userinput>c++ -o foobar foobar.cc</userinput></screen>
</informalexample>

<para>Each of these will both produce an executable
<filename>foobar</filename> from the C++ source file
<filename>foobar.cc</filename>. Note that, on Unix systems, C++
source files traditionally end in <filename>.C</filename>,
<filename>.cxx</filename> or <filename>.cc</filename>, rather than
the <trademark>MS-DOS</trademark> style <filename>.cpp</filename>
(which was already used for something else). <command>gcc</command>
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 <filename>.cpp</filename> with
impunity!</para>

</listitem>
</varlistentry>
</variablelist>
  
<sect1>
<title>Common <command>cc</command> Queries and Problems</title>

<para>Q. I am trying to write a program which uses the
<function>sin()</function> function and I get an error like this.
What does it mean?
<informalexample>
<screen>/var/tmp/cc0143941.o: Undefined symbol `_sin' referenced from text segment</screen>
</informalexample>
</para>
  
<para>A. When using mathematical functions like
<function>sin()</function>, you have to tell <command>cc</command> to
link in the math library, like so:
<informalexample>
<screen>$ <userinput>cc -o foobar foobar.c -lm</userinput></screen>
</informalexample></para>

<para>Q. All right, I wrote this simple program to practice using
<option>-lm</option>. All it does is raise 2.1 to the power of 6.
<informalexample>
<programlisting>#include &lt;stdio.h&gt;

int main() {
	float f;

	f = pow(2.1, 6);
	printf("2.1 ^ 6 = %f\n", f);
	return 0;
}</programlisting>
</informalexample>
and I compiled it as:
<informalexample>
<screen>$ <userinput>cc temp.c -lm</userinput></screen>
</informalexample>
like you said I should, but I get this when I run it:
<informalexample>
<screen>$ <userinput>./a.out</userinput>
2.1 ^ 6 = 1023.000000</screen>
</informalexample>
</para>
  
<para>This is <emphasis>not</emphasis> the right answer! What is
going on?</para>

<para>A. When the compiler sees you call a function, it checks if it
has already seen a prototype for it. If it has not, it assumes the
function returns an <type>int</type>, which is
definitely not what you want here.</para>

<para>Q. So how do I fix this?</para>
  
<para>A. The prototypes for the mathematical functions are in
<filename>math.h</filename>. If you include this file, the compiler
will be able to find the prototype and it will stop doing strange
things to your calculation!
<informalexample>
<programlisting>#include &lt;math.h&gt;
#include &lt;stdio.h&gt;

int main() {
...</programlisting>
</informalexample>
</para>
  
<para>After recompiling it as you did before, run it:
<informalexample>
<screen>$ <userinput>./a.out</userinput>
2.1 ^ 6 = 85.766121</screen>
</informalexample>
</para>
  
<para>If you are using any of the mathematical functions,
<emphasis>always</emphasis> include <filename>math.h</filename> and
remember to link in the math library.</para>

<para>Q. I compiled a file called <filename>foobar.c</filename> and I
cannot find an executable called <filename>foobar</filename>. Where's
it gone?</para>

<para>A. Remember, <command>cc</command> will call the executable
<filename>a.out</filename> unless you tell it differently. Use the
<option>-o&nbsp;<replaceable>filename</replaceable></option> option:
<informalexample>
<screen>$ <userinput>cc -o foobar foobar.c</userinput></screen>
</informalexample>
</para>

<para>Q. OK, I have an executable called <filename>foobar</filename>,
I can see it when I run <command>ls</command>, but when I type in
<command>foobar</command> at the command prompt it tells me there is
no such file. Why can it not find it?</para>

<para>A. Unlike <trademark>MS-DOS</trademark>, Unix does not look in the
current directory when it is trying to find out which executable you
want it to run, unless you tell it to. Either type
<command>./foobar</command>, which means <quote>run the file called
<filename>foobar</filename> in the current directory</quote>, or
change your <systemitem class=environvar>PATH</systemitem>
environment variable so that it looks something like
<informalexample>
<screen>bin:/usr/bin:/usr/local/bin:.</screen>
</informalexample>
The dot at the end means <quote>look in the current directory if it is not in
any of the others</quote>.</para>
  
<para>Q. I called my executable <filename>test</filename>, but
nothing happens when I run it. What is going on?</para>

<para>A. Most Unix systems have a program called
<command>test</command> in <filename>/usr/bin</filename> and the
shell is picking that one up before it gets to checking the current
directory. Either type:
<informalexample>
<screen>$ <userinput>./test</userinput></screen>
</informalexample>
or choose a better name for your program!</para>
  
<para>Q. I compiled my program and it seemed to run all right at
first, then there was an error and it said something about <errorname>core
dumped</errorname>. What does that mean?</para>

<para>A. The name <firstterm>core dump</firstterm> 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 <filename>core</filename>, which the programmer
could then pore over to find out what went wrong.</para>

<para>Q. Fascinating stuff, but what I am supposed to do now?</para>
  
<para>A. Use <command>gdb</command> to analyse the core (see <xref
linkend="debugging">).</para>
  
<para>Q. When my program dumped core, it said something about a
<errorname>segmentation fault</errorname>. What's that?</para>

<para>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.</para>
  
<para>Common causes for this are:
<itemizedlist>
<listitem><para>Trying to write to a <symbol>NULL</symbol> pointer, eg
<programlisting>char *foo = NULL;
strcpy(foo, "bang!");</programlisting>
</para></listitem>

<listitem><para>Using a pointer that hasn't been initialised, eg
<programlisting>char *foo;
strcpy(foo, "bang!");</programlisting>
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.</para></listitem>

<listitem><para>Trying to access past the end of an array, eg
<programlisting>int bar[20];
bar[27] = 6;</programlisting></para></listitem>

<listitem><para> Trying to store something in read-only memory, eg
<programlisting>char *foo = "My string";
strcpy(foo, "bang!");</programlisting>
Unix compilers often put string literals like
<literal>"My string"</literal> into
read-only areas of memory.</para></listitem>

<listitem><para>Doing naughty things with
<function>malloc()</function> and <function>free()</function>, eg
<programlisting>char bar[80];
free(bar);</programlisting>
or
<programlisting>char *foo = malloc(27);
free(foo);
free(foo);</programlisting>
</para></listitem>

</itemizedlist></para>

<para>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.</para>
  
<para>Q. Sometimes when I get a core dump it says <errorname>bus
error</errorname>. It says in my Unix book that this means a hardware
problem, but the computer still seems to be working. Is this
true?</para>

<para>A. No, fortunately not (unless of course you really do have a hardware
problem&hellip;). This is usually another way of saying that you
accessed memory in a way you shouldn't have.</para>
  
<para>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?</para>
  
<para>A. Yes, just go to another console or xterm, do
<screen>$ <userinput>ps</userinput></screen>
to find out the process ID of your program, and do
<screen>$ <userinput>kill -ABRT <replaceable>pid</replaceable></userinput></screen>
where <parameter><replaceable>pid</replaceable></parameter> is the
process ID you looked up.</para>
  
<para>This is useful if your program has got stuck in an infinite
loop, for instance. If your program happens to trap
<symbol>SIGABRT</symbol>, there are several other signals which have
a similar effect.</para>

</sect1>
</chapter>


<chapter>
<title>Make</title>

<sect1>
<title>What is <command>make</command>?</title>

<para>When you're working on a simple program with only one or two source
files, typing in
<screen>$ <userinput>cc file1.c file2.c</userinput></screen>
is not too bad, but it quickly becomes very tedious when there are
several files&mdash;and it can take a while to compile, too.</para>
  
<para>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:
<screen>$ <userinput>cc file1.o file2.o</userinput> &hellip; <userinput>file37.c</userinput> &hellip</screen>
if we'd changed <filename>file37.c</filename>, but not any of the
others, since the last time we compiled.  This may speed up the
compilation quite a bit, but  doesn't solve the typing
problem.</para>

<para>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.</para>
  
<para>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?</para>
  
<para>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.</para>
  
<para>This program is called <command>make</command>. It reads in a
file, called a <firstterm>makefile</firstterm>, 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 <quote>if <filename>fromboz.o</filename> is older than
<filename>fromboz.c</filename>, that means someone must have changed
<filename>fromboz.c</filename>, so it needs to be
re-compiled.</quote> The makefile also has rules telling make
<emphasis>how</emphasis> to re-compile the source file, making it a
much more powerful tool.</para>

<para>Makefiles are typically kept in the same directory as the
source they apply to, and can be called
<filename>makefile</filename>, <filename>Makefile</filename> or
<filename>MAKEFILE</filename>. Most programmers use the name
<filename>Makefile</filename>, as this puts it near the top of a
directory listing, where it can easily be seen.<footnote><para>They
don't use the <filename>MAKEFILE</filename> form as block capitals
are often used for documentation files like
<filename>README</filename>.</para></footnote></para>
  
</sect1>

<sect1>
<title>Example of using <command>make</command></title>

<para>Here's a very simple make file:
<programlisting>foo: foo.c
	cc -o foo foo.c</programlisting>
It consists of two lines, a dependency line and a creation line.</para>
  
<para>The dependency line here consists of the name of the program
(known as the <firstterm>target</firstterm>), followed by a colon,
then whitespace, then the name of the source file. When
<command>make</command> reads this line, it looks to see if
<filename>foo</filename> exists; if it exists, it compares the time
<filename>foo</filename> was last modified to the time
<filename>foo.c</filename> was last modified. If
<filename>foo</filename> does not exist, or is older than
<filename>foo.c</filename>, it then looks at the creation line to
find out what to do. In other words, this is the rule for working out
when <filename>foo.c</filename> needs to be re-compiled.</para>

<para>The creation line starts with a <token>tab</token> (press the
<keycap>tab</keycap> key) and then the command you would type to
create <filename>foo</filename> if you were doing it at a command
prompt. If <filename>foo</filename> is out of date, or does not
exist, <command>make</command> then executes this command to create
it. In other words, this is the rule which tells make how to
re-compile <filename>foo.c</filename>.</para>

<para>So, when you type <userinput>make</userinput>, it will make
sure that <filename>foo</filename> is up to date with respect to your
latest changes to <filename>foo.c</filename>. This principle can be
extended to <filename>Makefile</filename>s with hundreds of
targets&mdash;in fact, on FreeBSD, it is possible to compile the
entire operating system just by typing <userinput>make
world</userinput> in the appropriate directory!</para>

<para>Another useful property of makefiles is that the targets don't have
to be programs. For instance, we could have a make file that looks
like this:
<programlisting>foo: foo.c
	cc -o foo foo.c

install:
	cp foo /home/me</programlisting></para>
  
<para>We can tell make which target we want to make by typing:
<screen>$ <userinput>make <replaceable>target</replaceable></userinput></screen>
<command>make</command> will then only look at that target and ignore any
others. For example, if we type <userinput>make foo</userinput> with the 
makefile above, make will ignore the <action>install</action> target.</para>
  
<para>If we just type <userinput>make</userinput> on its own, make
will always look at the first target and then stop without looking at
any others. So if we typed <userinput>make</userinput> here, it will
just go to the <action>foo</action> target, re-compile
<filename>foo</filename> if necessary, and then stop without going on
to the <action>install</action> target.</para>

<para>Notice that the <action>install</action> 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 <userinput>make install</userinput>. In this case, it will
copy <filename>foo</filename> into the user's home directory. This is
often used by application makefiles, so that the application can be
installed in the correct directory when it has been correctly
compiled.</para>

<para>This is a slightly confusing subject to try and explain. If you
don't quite understand how <command>make</command> works, the best
thing to do is to write a simple program like <quote>hello
world</quote> 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 <command>touch</command> command is
very useful here&mdash;it changes the date on a file without you
having to edit it.</para>
  
</sect1>

<sect1>
<title>FreeBSD Makefiles</title>

<para>Makefiles can be rather complicated to write. Fortunately,
BSD-based systems like FreeBSD come with some very powerful ones as
part of the system.  One very good example of this is the FreeBSD
ports system. Here's the essential part of a typical ports
<filename>Makefile</filename>:
<programlisting>MASTER_SITES=   ftp://freefall.cdrom.com/pub/FreeBSD/LOCAL_PORTS/
DISTFILES=      scheme-microcode+dist-7.3-freebsd.tgz

.include &lt;bsd.port.mk&gt;</programlisting></para>
  
<para>Now, if we go to the directory for this port and type
<userinput>make</userinput>, the following happens:</para>

<procedure>
<step><para>A check is made to see if the source code for this port is
already on the system.</para></step>

<step><para>If it isn't, an FTP connection to the URL in
<symbol>MASTER_SITES</symbol> is set up to download the
source.</para></step>

<step><para>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.</para></step>

<step><para>Any changes required to make the source work on FreeBSD are
applied&mdash;this is known as <firstterm>patching</firstterm>.</para></step>

<step><para>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&mdash;this is where they are given the information in the
FreeBSD ports scenario).</para></step>

<step><para>The source code for the program is compiled. In effect,
we change to the directory where the source was unpacked and do
<command>make</command>&mdash;the program's own make file has the
necessary information to build the program.</para></step>

<step><para>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 <userinput>make install</userinput>. 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 <database>package
database</database>, so that the port can easily be uninstalled later
if we change our mind about it.</para></step>

</procedure>
  
<para>Now I think you'll agree that's rather impressive for a four
line script!</para>

<para>The secret lies in the last line, which tells
<command>make</command> to look in the system makefile called
<filename>bsd.port.mk</filename>. It's easy to overlook this line,
but this is where all the clever stuff comes from&mdash;someone has
written a makefile that tells <command>make</command> to do all the
things above (plus a couple of other things I didn't mention,
including handling any errors that may occur) and anyone can get
access to that just by putting a single line in their own make
file!</para>

<para>If you want to have a look at these system makefiles, they're
in <filename>/usr/share/mk</filename>, but it's probably best to wait
until you've had a bit of practice with makefiles, as they are very
complicated (and if you do look at them, make sure you have a flask
of strong coffee handy!)</para>

</sect1>

<sect1>
<title>More advanced uses of <command>make</command></title>

<para><command>Make</command> is a very powerful tool, and can do much
more than the simple example above shows. Unfortunately, there are
several different versions of <command>make</command>, and they all
differ considerably. The best way to learn what they can do is
probably to read the documentation&mdash;hopefully this introduction will
have given you a base from which you can do this.</para>

<para>The version of make that comes with FreeBSD is the <application>Berkeley
make</application>; there is a tutorial for it in
<filename>/usr/share/doc/psd/12.make</filename>. To view it, do
<screen>$ <userinput>zmore paper.ascii.gz</userinput></screen>
in that directory.</para>
  
<para>Many applications in the ports use <application>GNU
make</application>, which has a very good set of <quote>info</quote>
pages. If you have installed any of these ports, <application>GNU
make</application> will automatically have been installed as
<command>gmake</command>. It's also available as a port and package
in its own right.</para>

<para>To view the info pages for <application>GNU make</application>,
you will have to edit the <filename>dir</filename> file in the
<filename>/usr/local/info</filename> directory to add an entry for
it. This involves adding a line like
<programlisting> * Make: (make).                 The GNU Make utility.</programlisting>
to the file. Once you have done this, you can type
<userinput>info</userinput> and then select
<guimenuitem>make</guimenuitem> from the menu (or in
<application>Emacs</application>, do <userinput>C-h
i</userinput>).</para>

</sect1>
</chapter>

<chapter id="debugging">
<title>Debugging</title>

<sect1>
<title>The Debugger</title>

<para>The debugger that comes with FreeBSD is called
<command>gdb</command> (<application>GNU
debugger</application>). You start it up by typing
<screen>$ <userinput>gdb <replaceable>progname</replaceable></userinput></screen>
although most people prefer to run it inside
<application>Emacs</application>. You can do this by:
<screen><userinput>M-x gdb RET <replaceable>progname</replaceable> RET</userinput></screen></para>
  
<para>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. 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.</para>

<para><command>gdb</command> 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.</para>

<para>Finally, if you find its text-based command-prompt style
off-putting, there's a graphical front-end for it <ulink
URL="../../ports/devel.html">xxgdb</ulink>
in the ports collection.</para>

<para>This section is intended to be an introduction to using
<command>gdb</command> and does not cover specialised topics such as
debugging the kernel.</para>
  
</sect1>

<sect1>
<title>Running a program in the debugger</title>

<para>You'll need to have compiled the program with the
<option>-g</option> option to get the most out of using
<command>gdb</command>. 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:
<screen>&hellip; (no debugging symbols found) &hellip;</screen>when
<command>gdb</command> starts up, you'll know that the program wasn't
compiled with the <option>-g</option> option.</para>
  
<para>At the <command>gdb</command> prompt, type <userinput>break
main</userinput>. 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 <userinput>run</userinput> to start the
program&mdash;it will start at the beginning of the set-up code and
then get stopped by the debugger when it calls
<function>main()</function>. (If you've ever wondered where
<function>main()</function> gets called from, now you know!).</para>

<para>You can now step through the program, a line at a time, by
pressing <command>n</command>.  If you get to a function call, you can
step into it by pressing <command>s</command>. Once you're in a
function call, you can return from stepping into a function call by
pressing <command>f</command>. You can also use <command>up</command> and
<command>down</command> to take a quick look at the caller.</para>

<para>Here's a simple example of how to spot a mistake in a program
with <command>gdb</command>. This is our program (with a deliberate
mistake):
<programlisting>#include &lt;stdio.h&gt;

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;
}</programlisting>
</para>
  
<para>This program sets <symbol>i</symbol> to be <literal>5</literal>
and passes it to a function <function>bazz()</function> which prints
out the number we gave it.</para>

<para>When we compile and run the program we get
<screen>$ <userinput>cc -g -o temp temp.c</userinput>
$ <userinput>./temp</userinput>
This is my program
anint = 4231</screen></para>
  
<para>That wasn't what we expected! Time to see what's going
on!<screen>$ <userinput>gdb temp</userinput>
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) <userinput>break main</>				<lineannotation>Skip the set-up code</>
Breakpoint 1 at 0x160f: file temp.c, line 9.	<lineannotation><command>gdb</command> puts breakpoint at <function>main()</></>
(gdb) <userinput>run</>					<lineannotation>Run as far as <function>main()</></>
Starting program: /home/james/tmp/temp		<lineannotation>Program starts running</>

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

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

<para><screen>(gdb) <userinput>up</>					<lineannotation>Move up call stack</>
#1  0x1625 in main () at temp.c:11		<lineannotation><command>gdb</command> displays stack frame</>
(gdb) <userinput>p i</>					<lineannotation>Show us the value of <symbol>i</></>
$1 = 4231					<lineannotation><command>gdb</command> displays <literal>4231</></></screen>
Oh dear! Looking at the code, we forgot to initialise
<symbol>i</symbol>. We meant to put
<programlisting><lineannotation>&hellip;</>
main() {
	int i;

	i = 5;
	printf("This is my program\n");
<lineannotation>&hellip</></programlisting>
but we left the <literal>i=5;</literal> line out.  As we didn't
initialise <symbol>i</symbol>, it had whatever number happened to be
in that area of memory when the program ran, which in this case
happened to be <literal>4231</literal>.</para>

<note><para><command>gdb</command> displays the stack frame
every time we go into or out of a function, even if we're using
<command>up</command> and <command>down</command> 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).</para></note>

</sect1>

<sect1>
<title>Examining a core file</title>

<para>A core file is basically a file which contains the complete
state of the process when it crashed. In <quote>the good old
days</quote>, 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 <filename><replaceable>progname</>.core</> instead of just
<filename>core</filename>, to make it clearer which program a core
file belongs to.</para>

<para>To examine a core file, start up <command>gdb</command> in the
usual way. Instead of typing <command>break</command> or
<command>run</command>, type
<screen>(gdb) <userinput>core <replaceable>progname</replaceable>.core</userinput></screen>
If you're not in the same directory as the core file, you'll have to
do <userinput>dir /path/to/core/file</userinput> first.</para>
  
<para>You should see something like this:
<screen>$ <userinput>gdb a.out</userinput>
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) <userinput>core a.out.core</userinput>
Core was generated by `a.out'.
Program terminated with signal 11, Segmentation fault.
Cannot access memory at address 0x7020796d.
#0  0x164a in bazz (anint=0x5) at temp.c:17
(gdb)</screen></para>
  
<para>In this case, the program was called
<filename>a.out</filename>, so the core file is called
<filename>a.out.core</filename>. 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 <function>bazz</function>.</para>

<para>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 <command>bt</command> command causes
<command>gdb</command> to print out a back-trace of the call
stack:
<screen>(gdb) <userinput>bt</userinput>
#0  0x164a in bazz (anint=0x5) at temp.c:17
#1  0xefbfd888 in end ()
#2  0x162c in main () at temp.c:11
(gdb)</screen>The <function>end()</function> function is called when
a program crashes; in this case, the <function>bazz()</function>
function was called from <function>main()</function>.</para>

</sect1>

<sect1>
<title>Attaching to a running program</title>

<para>One of the neatest features about <command>gdb</command> 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.</para>

<para>What you do is start up another <command>gdb</command>, use
<command>ps</command> to find the process ID for the child, and
do<screen>(gdb) <userinput>attach <replaceable>pid</replaceable></userinput></screen>  
in <command>gdb</command>, and then debug as usual.</para>
  
<para><quote>That's all very well,</quote> you're probably thinking,
<quote>but by the time I've done that, the child process will be over
the hill and far away</quote>. Fear not, gentle reader, here's how to
do it (courtesy of the <command>gdb</command> info pages):
<screen><lineannotation>&hellip</lineannotation>
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 */
	<lineannotation>&hellip</lineannotation>
} else {			/* parent */
	<lineannotation>&hellip</lineannotation></screen>
Now all you have to do is attach to the child, set
<symbol>PauseMode</symbol> to <literal>0</literal>, and
wait for the <function>sleep()</function> call to return!</para>
  
</sect1>
</chapter>

<chapter id="emacs">
<title>Using Emacs as a Development Environment</title>

<sect1>
<title>Emacs</title>

<para>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.<footnote><para>At least, not unless you pay out very large sums
of money.</para></footnote> 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.</para>

<para>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&mdash;I'd recommend 8MB in
text mode and 16MB in X as the bare minimum to get reasonable
performance.</para>

<para>Emacs is basically a highly customisable editor&mdash;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.</para>

<para>It's impossible even to summarise everything Emacs can do here, but
here are some of the features of interest to developers:
<itemizedlist>

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

<listitem><para>Pull-down menus and online help.</para></listitem>

<listitem><para>Language-dependent syntax highlighting and
indentation.</para></listitem>

<listitem><para>Completely customisable.</para></listitem>

<listitem><para>You can compile and debug programs within
Emacs.</para></listitem>

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

<listitem><para>Friendly-ish front-end to the <command>info</command>
program used for reading GNU hypertext documentation, including the
documentation on Emacs itself.</para></listitem>

<listitem><para>Friendly front-end to <command>gdb</command>,
allowing you to look at the source code as you step through your
program.</para></listitem>

<listitem><para>You can read Usenet news and mail while your program
is compiling.</para></listitem>

</itemizedlist>And doubtless many more that I've overlooked.</para>

<para>Emacs can be installed on FreeBSD using <ulink
URL="../../ports/editors.html">the Emacs
port</ulink>.</para>

<para>Once it's installed, start it up and do <userinput>C-h
t</userinput> to read an Emacs tutorial&mdash;that means hold down
the <keycap>control</keycap> key, press <keycap>h</keycap>, let go of
the <keycap>control</keycap> key, and then press <keycap>t</keycap>.
(Alternatively, you can you use the mouse to select <guimenuitem>Emacs
Tutorial</guimenuitem> from the <guimenu>Help</guimenu> menu).</para>

<para>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
<quote><literal>M-x replace-s RET foo RET bar RET</literal></quote>
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.</para>

<para>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.</para>

<para>If you can't remember what a particular combination of keys
does, select <guimenuitem>Describe Key</guimenuitem> from the
<guimenu>Help</guimenu> menu and type it in&mdash;Emacs will tell you
what it does. You can also use the <guimenuitem>Command
Apropos</guimenuitem> menu item to find out all the commands which
contain a particular word in them, with the key binding next to
it.</para>

<para>By the way, the expression above means hold down the
<keysym>Meta</keysym> key, press <keysym>x</keysym>, release the
<keysym>Meta</keysym> key, type <userinput>replace-s</userinput>
(short for <literal>replace-string</literal>&mdash;another feature of
Emacs is that you can abbreviate commands), press the
<keysym>return</keysym> key, type <userinput>foo</userinput> (the
string you want replaced), press the <keysym>return</keysym> key,
type bar (the string you want to replace <literal>foo</literal> with)
and press <keysym>return</keysym> again. Emacs will then do the
search-and-replace operation you've just requested.</para>

<para>If you're wondering what on earth the <keysym>Meta</keysym> key
is, it's a special key that many Unix workstations have.
Unfortunately, PC's don't have one, so it's usually the
<keycap>alt</keycap> key (or if you're unlucky, the <keysym>escape</keysym>
key).</para>

<para>Oh, and to get out of Emacs, do <command>C-x C-c</command>
(that means hold down the <keysym>control</keysym> key, press
<keysym>x</keysym>, press <keysym>c</keysym> and release the
<keysym>control</keysym> 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 <command>C-z</command> is the usual way
to leave Emacs&mdash;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).</para>

</sect1>

<sect1>
<title>Configuring Emacs</title>

<para>Emacs does many wonderful things; some of them are built in,
some of them need to be configured.</para>

<para>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!).</para>

<para>The best way to learn Emacs Lisp is to download the <ulink
URL="ftp://prep.ai.mit.edu:pub/gnu/elisp-manual-19-2.4.tar.gz">Emacs
Tutorial</ulink></para>

<para>However, there's no need to actually know any Lisp to get
started with configuring Emacs, as I've included a sample
<filename>.emacs</filename> 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.</para>

</sect1>

<sect1>
<title>A sample <filename>.emacs</filename> file</title>

<para>Unfortunately, there's far too much here to explain it in detail;
however there are one or two points worth mentioning.</para>
  
<para>
<itemizedlist>

<listitem><para>Everything beginning with a <literal>;</> is a
comment and is ignored by Emacs.</para></listitem>

<listitem><para>In the first line, the
<literal>-*-&nbsp;Emacs-Lisp&nbsp;-*-</literal> is so that we can
edit the <filename>.emacs</filename> 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
<filename>.emacs</filename>. </para></listitem>

<listitem><para>The <keysym>tab</keysym> 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
<token>tab</token> character in whatever you're writing, hold the
<keysym>control</keysym> key down while you're pressing the
<keysym>tab</keysym> key.</para></listitem>

<listitem><para>This file supports syntax highlighting for C, C++,
Perl, Lisp and Scheme, by guessing the language from the
filename.</para></listitem>

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

<listitem><para> 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 
<screen>$ <userinput>emacsclient <replaceable>filename</replaceable></userinput></screen>
and then you can edit the file in your Emacs!<footnote><para>Many
Emacs users set their <systemitem
class=environvar>EDITOR</systemitem> environment to
<literal>emacsclient</literal> so this happens every time they need
to edit a file.</para></footnote></para></listitem>

</itemizedlist>
</para>
  
<example>
<title>A sample <filename>.emacs</filename> file</title>
<screen>;; -*-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-&lt;")
(global-set-key [C-end] "\M-&gt;")
(global-set-key [C-prior] "\M-&lt;")
(global-set-key [C-next] "\M-&gt;")

;; 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 &lt;CR&gt; 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") </screen>

<screen>(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)))</screen>

<screen>;; 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) ".")
</screen>
</example>
  
</sect1>

<sect1>
<title>Extending the Range of Languages Emacs Understands</title>

<para>Now, this is all very well if you only want to program in the
languages already catered for in the <filename>.emacs</filename> file
(C, C++, Perl, Lisp and Scheme), but what happens if a new language
called <quote>whizbang</quote> comes out, full of exciting
features?</para>

<para>The first thing to do is find out if whizbang
comes with any files that tell Emacs about the language. These
usually end in <filename>.el</filename>, short for <quote>Emacs
Lisp</quote>. For example, if whizbang is a FreeBSD
port, we can locate these files by doing
<screen>$ <userinput>find /usr/ports/lang/whizbang -name "*.el" -print</userinput></screen>
and install them by copying them into the Emacs site Lisp directory. On
FreeBSD 2.1.0-RELEASE, this is
<filename>/usr/local/share/emacs/site-lisp</filename>.</para>

<para>So for example, if the output from the find command was
<screen>/usr/ports/lang/whizbang/work/misc/whizbang.el</screen>
we would do
<screen>$ <userinput>cp /usr/ports/lang/whizbang/work/misc/whizbang.el /usr/local/share/emacs/site-lisp</userinput></screen>
</para>
  
<para>Next, we need to decide what extension whizbang source files
have. Let's say for the sake of argument that they all end in
<filename>.wiz</filename>. We need to add an entry to our
<filename>.emacs</filename> file to make sure Emacs will be able to
use the information in <filename>whizbang.el</filename>.</para>

<para>Find the <symbol>auto-mode-alist entry</symbol> in
<filename>.emacs</filename> and add a line for whizbang, such
as:
<programlisting><lineannotation>&hellip;</>
("\\.lsp$" . lisp-mode)
("\\.wiz$" . whizbang-mode)
("\\.scm$" . scheme-mode)
<lineannotation>&hellip;</></programlisting>  
This means that Emacs will automatically go into
<function>whizbang-mode</function> when you edit a file ending in
<filename>.wiz</filename>.</para>

<para>Just below this, you'll find the
<symbol>font-lock-auto-mode-list</symbol> entry. Add
<function>whizbang-mode</function> to it like so:
<programlisting>;; 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")</programlisting>
This means that Emacs will always enable
<function>font-lock-mode</function> (ie syntax highlighting) when
editing a <filename>.wiz</filename> file.</para>

<para>And that's all that's needed. If there's anything else you want
done automatically when you open up a <filename>.wiz</filename> file,
you can add a <function>whizbang-mode hook</function> (see
<function>my-scheme-mode-hook</function> for a simple example that
adds <function>auto-indent</function>).</para>
  
</sect1>
</chapter>

<chapter>
<title>Further Reading</title>

<itemizedlist>
<listitem><para>Brian Harvey and Matthew Wright
<emphasis>Simply Scheme</emphasis>
MIT 1994.<!-- <br> -->
ISBN 0-262-08226-8</para></listitem>

<listitem><para>Randall Schwartz
<emphasis>Learning Perl</emphasis>
O'Reilly 1993<!-- <br> -->
ISBN 1-56592-042-2</para></listitem>

<listitem><para>Patrick Henry Winston and Berthold Klaus Paul Horn
<emphasis>Lisp (3rd Edition)</emphasis>
Addison-Wesley 1989<!-- <br> -->
ISBN 0-201-08319-1</para></listitem>

<listitem><para>Brian W. Kernighan and Rob Pike
<emphasis>The Unix Programming Environment</emphasis>
Prentice-Hall 1984<!-- <br> -->
ISBN 0-13-937681-X</para></listitem>

<listitem><para>Brian W. Kernighan and Dennis M. Ritchie
<emphasis>The C Programming Language (2nd Edition)</emphasis>
Prentice-Hall 1988<!-- <br> -->
ISBN 0-13-110362-8</para></listitem>

<listitem><para>Bjarne Stroustrup
<emphasis>The C++ Programming Language</emphasis>
Addison-Wesley 1991<!-- <br> -->
ISBN 0-201-53992-6</para></listitem>

<listitem><para>W. Richard Stevens
<emphasis>Advanced Programming in the Unix Environment</emphasis>
Addison-Wesley 1992<!-- <br> -->
ISBN 0-201-56317-7</para></listitem>

<listitem><para>W. Richard Stevens
<emphasis>Unix Network Programming</emphasis>
Prentice-Hall 1990<!-- <br> -->
ISBN 0-13-949876-1</para></listitem>

</itemizedlist>

</chapter>
</book>