Capítulo 12. Programação

Índice

12.1. O script shell
12.1.1. POSIX shell compatibility
12.1.2. Parâmetros da shell
12.1.3. Condicionais da shell
12.1.4. Ciclos da shell
12.1.5. A sequência de processamento da linha de comandos da shell
12.1.6. Utility programs for shell script
12.1.7. Shell script dialog
12.1.8. Shell script example with zenity
12.2. Make
12.3. C
12.3.1. Programa C simples (gcc)
12.4. Depuração
12.4.1. Execução gdb básica
12.4.2. Depurar o pacote Debian
12.4.3. Obtaining backtrace
12.4.4. Advanced gdb commands
12.4.5. Depurar Erros do X
12.4.6. Verificar a dependência em bibliotecas
12.4.7. Ferramentas de detecção de fugas de memória
12.4.8. Ferramentas de análise de código estático
12.4.9. Disassemble binary
12.5. Flex — um Lex melhor.
12.6. Bison — um Yacc melhor
12.7. Autoconf
12.7.1. Compilar e instalar o programa
12.7.2. Desinstalar o programa
12.8. Perl short script madness
12.9. Web
12.10. A tradução do código fonte
12.11. Criando um pacote Debian

I provide some pointers for people to learn programming on the Debian system enough to trace the packaged source code. Here are notable packages and corresponding documentation packages for programing.

Tabela 12.1. Lista de pacotes para ajudar a programar

pacote popcon tamanho documentação
autoconf * V:4, I:25 2256 "info autoconf" disponibilizado por autoconf-doc
automake * V:3, I:21 1812 "info automake" disponibilizado por automake1.10-doc
bash * V:91, I:99 3536 "info bash" disponibilizado por bash-doc
bison * V:2, I:15 1504 "info bison" disponibilizado por bison-doc
cpp * V:38, I:82 32 "info cpp" disponibilizado por cpp-doc
ddd * V:0.3, I:2 3852 "info ddd" disponibilizado por ddd-doc
exuberant-ctags * V:1.2, I:5 284 exuberant-ctags(1)
flex * V:2, I:15 1352 "info flex" disponibilizado por flex-doc
gawk * V:28, I:32 2172 "info gawk" disponibilizado por gawk-doc
gcc * V:17, I:67 28 "info gcc" disponibilizado por gcc-doc
gdb * V:4, I:22 4812 "info gdb" disponibilizado por gdb-doc
gettext * V:8, I:46 7272 "info gettext" disponibilizado por gettext-doc
gfortran * V:0.9, I:6 8 "info gfortran" disponibilizado por gfortran-doc (Fortran 95)
gpc * V:0.07, I:0.5 8 "info gpc" disponibilizado por gpc-doc (Pascal)
fpc * I:0.4 40 fpc(1) e html por fp-docs (Pascal)
glade * V:0.3, I:2 1652 help provided via menu (UI Builder)
glade-gnome * V:0.09, I:1.2 508 help provided via menu (UI Builder)
libc6 * V:97, I:99 10012 "info libc" disponibilizado por glibc-doc e glibc-doc-reference
make * V:21, I:72 1220 "info make" disponibilizado por make-doc
xutils-dev * V:1.7, I:15 1728 imake(1), xmkmf(1), etc.
mawk * V:66, I:99 244 mawk(1)
perl * V:88, I:99 18528 perl(1) e páginas html disponibilizadas por perl-doc e perl-doc-html
python * V:62, I:97 736 python(1) e páginas html disponibilizadas por python-doc
tcl8.4 * V:8, I:46 3332 tcl(3) and detail manual pages provided by tcl8.4-doc
tk8.4 * V:5, I:34 2712 tk(3) and detail manual pages provided by tk8.4-doc
ruby * V:9, I:24 120 ruby(1) and interactive reference provided by ri
vim * V:15, I:33 1792 help(F1) menu disponibilizado por vim-doc
susv2 * I:0.03 48 fetch "The Single Unix Specifications v2"
susv3 * I:0.07 48 fetch "The Single Unix Specifications v3"

Online references are available by typing "man name" after installing manpages and manpages-dev packages. Online references for the GNU tools are available by typing "info program_name" after installing the pertinent documentation packages. You may need to include the contrib and non-free archives in addition to the main archive since some GFDL documentations are not considered to be DSFG compliant.

[Atenção] Atenção

Do not use "test" as the name of an executable test file. "test" is a shell builtin.

[Cuidado] Cuidado

You should install software programs directly compiled from source into "/usr/local" or "/opt" to avoid collision with system programs.

[Dica] Dica

Code examples of creating "Song 99 Bottles of Beer" should give you good idea of practically all the programming languages.

12.1. O script shell

The shell script is a text file with the execution bit set and contains the commands in the following format.

#!/bin/sh
 ... command lines

The first line specifies the shell interpreter which read and execute this file contents.

Reading shell scripts is the best way to understand how a Unix-like system works. Here, I give some pointers and reminders for shell programming. See "Shell Mistakes" (http://www.greenend.org.uk/rjk/2001/04/shell.html) to learn from mistakes.

Unlike shell interactive mode (see Secção 1.5, “O simples comando de shell” and Secção 1.6, “Processamento de texto estilo Unix”), shell scripts frequently use parameters, conditionals, and loops.

12.1.1. POSIX shell compatibility

Many system scripts may be interpreted by any one of POSIX shells (see Tabela 1.13, “Lista de programas da shell”). The default shell for the system is "/bin/sh" which is a symlink pointing to the actual program.

  • bash(1) for lenny or older
  • dash(1) for squeeze or newer

Avoid writing a shell script with bashisms or zshisms to make it portable among all POSIX shells. You can check it using checkbashisms(1).

Tabela 12.2. List of typical bashisms

Good: POSIX Avoid: bashism
if [ "$foo" = "$bar" ] ; then … if [ "$foo" == "$bar" ] ; then …
diff -u file.c.orig file.c diff -u file.c{.orig,}
mkdir /foobar /foobaz mkdir /foo{bar,baz}
funcname() { … } function funcname() { … }
formato octal: "\377" formato hexadecimal: "\xff"

The "echo" command must be used with following cares since its implementation differs among shell builtin and external commands.

  • Avoid using command option "-e" and "-E".
  • Avoid using any command options except "-n".
  • Avoid using escape sequences in the string since their handling varies.
[Nota] Nota

Although "-n option is not really POSIX syntax, it is generally accepted.

[Dica] Dica

Use the "printf" command instead of the "echo" command if you need to embed escape sequences in the output string.

12.1.2. Parâmetros da shell

Parâmetros de shell especiais são frequentemente usados no script shell.

Tabela 12.3. Lista de parâmetros da shel

parâmetro da shell valor
$0 nome da shell ou script de shell
$1 primeiro(1) argumento shell
$9 nono(9) argumento shell
$# número de parâmetros de posição
"$*" "$1 $2 $3 $4 … "
"$@" "$1" "$2" "$3" "$4" …
$? estado de saída do comando mais recente
$$ PID deste script shell
$! PID of most recently started background job

Basic parameter expansions to remember are followings.

Tabela 12.4. Lista de expansões de parâmetros de shell

formato da expressão do parâmetro valor se var estiver definido valor se var não estiver definido
${var:-string} "$var" "string"
${var:+string} "string" "null"
${var:=string} "$var" "string" (and run "var=string")
${var:?string} "$var" echo "string" para stderr (e termina com erro)

Aqui, os o caractere dois pontos ":" em todas estas operações é na realidade opcional.

  • with ":" = operator test for exist and not null
  • without ":" = operator test for exist only

Tabela 12.5. Lista de substituições de parâmetros de shell chave

formato de substituição de parâmetro resultado
${var%suffix} remover o padrão de sufixo menor
${var%%suffix} remover o padrão de sufixo maior
${var#prefix} remover o padrão de prefixo menor
${var##prefix} remover o padrão de prefixo maior

12.1.3. Condicionais da shell

Each command returns an exit status which can be used for conditional expressions.

  • Sucesso: 0 ("True")
  • Erro: não 0 ("False")
[Nota] Nota

"0" in the shell conditional context means "True", while "0" in the C conditional context means "False".

[Nota] Nota

"[" is the equivalent of the test command, which evaluates its arguments up to "]" as a conditional expression.

Basic conditional idioms to remember are followings.

  • "<command> && <if_success_run_this_command_too> || true"
  • "<command> || <if_not_success_run_this_command_too> || true"
  • A multi-line script snippet as the following
if [ <conditional_expression> ]; then
 <if_success_run_this_command>
else
 <if_not_success_run_this_command>
fi

Here trailing "|| true" was needed to ensure this shell script does not exit at this line accidentally when shell is invoked with "-e" flag.

Tabela 12.6. Lista de operadores de comparação de ficheiros na expressão condicional

equação condição para retornar o verdadeiro lógico
-e <ficheiro> <ficheiro> existe
-d <ficheiro> <ficheiro> existe e é um directório
-f <ficheiro> <ficheiro> existe e é um ficheiro normal
-w <ficheiro> <ficheiro> existe e pode-se escrever nele
-x <ficheiro> <ficheiro> existe e é executável
<file1> -nt <file2> <file1> is newer than <file2> (modification)
<file1> -ot <file2> <file1> is older than <file2> (modification)
<file1> -ef <file2> <file1> and <file2> are on the same device and the same inode number

Tabela 12.7. Lista de operadores de comparação de strings na expressão condicional

equação condição para retornar o verdadeiro lógico
-z <str> o comprimento de <str> é zero
-n <str> o comprimento de <str> não é zero
<str1> = <str2> <str1> and <str2> são iguais
<str1> != <str2> <str1> and <str2> não são iguais
<str1> < <str2> <str1> sorts before <str2> (locale dependent)
<str1> > <str2> <str1> sorts after <str2> (locale dependent)

Arithmetic integer comparison operators in the conditional expression are "-eq", "-ne", "-lt", "-le", "-gt", and "-ge".

12.1.4. Ciclos da shell

There are several loop idioms to use in POSIX shell.

  • "for x in foo1 foo2 … ; do command ; done" loops by assigning items from the list "foo1 foo2 …" to variable "x" and executing "command".
  • "while condition ; do command ; done" repeats "command" while "condition" is true.
  • "until condition ; do command ; done" repeats "command" while "condition" is not true.
  • "break" permite sair do ciclo.
  • "continue" enables to resume the next iteration of the loop.
[Dica] Dica

The C-language like numeric iteration can be realized by using seq(1) as the "foo1 foo2 …" generator.

12.1.5. A sequência de processamento da linha de comandos da shell

The shell processes a script roughly as the following sequence.

  • A shell lê uma linha.
  • The shell groups a part of the line as one token if it is within "…" or '…'.
  • The shell splits other part of a line into tokens by the following.

    • Whitespaces: <space> <tab> <newline>
    • Metacharacters: < > | ; & ( )
  • The shell checks the reserved word for each token to adjust its behavior if not within "…" or '…'.

    • reserved word: if then elif else fi for in while unless do done case esac
  • The shell expands alias if not within "…" or '…'.
  • The shell expands tilde if not within "…" or '…'.

    • "~" → current user's home directory
    • "~<user>" → <user>'s home directory
  • The shell expands parameter to its value if not within '…'.

    • parameter: "$PARAMETER" or "${PARAMETER}"
  • The shell expands command substitution if not within '…'.

    • "$( command )" → the output of "command"
    • "` command `" → the output of "command"
  • The shell expands pathname glob to matching file names if not within "…" or '…'.

    • * → quaisquer caracteres
    • ? → um caractere
    • […] → any one of the characters in ""
  • The shell looks up command from the following and execute it.

    • function definition
    • builtin command
    • executable file in "$PATH"
  • The shell goes to the next line and repeats this process again from the top of this sequence.

Single quotes within double quotes have no effect.

Executing "set -x" in the shell or invoking the shell with "-x" option make the shell to print all of commands executed. This is quite handy for debugging.

12.1.6. Utility programs for shell script

In order to make your shell program as portable as possible across Debian system, it is good idea to limit utility programs to ones provided by essential packages.

  • "aptitude search ~E" lists essential packages.
  • "dpkg -L <package_name> |grep '/man/man.*/'" lists manpages for commands offered by <package_name> package.

Tabela 12.8. List of packages containing small utility programs for shell scripts

pacote popcon tamanho descrição
coreutils * V:92, I:99 13828 utilitários de núcleo GNU
debianutils * V:93, I:99 260 utilitários variados específicos da Debian
bsdmainutils * V:81, I:99 768 colecção de mais utilitários do FreeBSD
bsdutils * V:77, I:99 196 utilitários básicos do 4.4BSD-Lite
moreutils * V:0.3, I:1.5 220 utilitários Unix adicionais

[Dica] Dica

Although moreutils may not exist ouside of Debian, it offers interesting small programs. Most notable one is sponge(8). See Secção 1.6.4, “Substituição global com expressões regulares”.

12.1.7. Shell script dialog

The user interface of a simple shell program can be improved from dull interaction by echo and read commands to more interactive one by using one of the so-called dialog program etc.

Tabela 12.9. Lista de programas de interface de utilizador

pacote popcon tamanho descrição
x11-utils * V:26, I:53 652 xmessage(1): display a message or query in a window (X)
whiptail * V:42, I:99 104 displays user-friendly dialog boxes from shell scripts (newt)
dialog * V:4, I:25 1592 displays user-friendly dialog boxes from shell scripts (ncurses)
zenity * V:8, I:41 4992 display graphical dialog boxes from shell scripts (gtk2.0)
ssft * V:0.01, I:0.11 152 Shell Scripts Frontend Tool (wrapper for zenity, kdialog, and dialog with gettext)
gettext * V:8, I:46 7272 "/usr/bin/gettext.sh": traduz mensagem

12.1.8. Shell script example with zenity

Here is a simple script which creates ISO image with RS02 data supplemented by dvdisaster(1).

#!/bin/sh -e
# gmkrs02 : Copyright (C) 2007 Osamu Aoki <osamu@debian.org>, Public Domain
#set -x
error_exit()
{
  echo "$1" >&2
  exit 1
}
# Initialize variables
DATA_ISO="$HOME/Desktop/iso-$$.img"
LABEL=$(date +%Y%m%d-%H%M%S-%Z)
if [ $# != 0 ] && [ -d "$1" ]; then
  DATA_SRC="$1"
else
  # Select directory for creating ISO image from folder on desktop
  DATA_SRC=$(zenity --file-selection --directory  \
    --title="Select the directory tree root to create ISO image") \
    || error_exit "Exit on directory selection"
fi
# Check size of archive
xterm -T "Check size $DATA_SRC" -e du -s $DATA_SRC/*
SIZE=$(($(du -s $DATA_SRC | awk '{print $1}')/1024))
if [ $SIZE -le 520 ] ; then
  zenity --info --title="Dvdisaster RS02" --width 640  --height 400 \
    --text="The data size is good for CD backup:\\n $SIZE MB"
elif [ $SIZE -le 3500 ]; then
  zenity --info --title="Dvdisaster RS02" --width 640  --height 400 \
    --text="The data size is good for DVD backup :\\n $SIZE MB"
else
  zenity --info --title="Dvdisaster RS02" --width 640  --height 400 \
    --text="The data size is too big to backup : $SIZE MB"
  error_exit "The data size is too big to backup :\\n $SIZE MB"
fi
# only xterm is sure to have working -e option
# Create raw ISO image
rm -f "$DATA_ISO" || true
xterm -T "genisoimage $DATA_ISO" \
  -e genisoimage -r -J -V "$LABEL" -o "$DATA_ISO" "$DATA_SRC"
# Create RS02 supplemental redundancy
xterm -T "dvdisaster $DATA_ISO" -e  dvdisaster -i "$DATA_ISO" -mRS02 -c
zenity --info --title="Dvdisaster RS02" --width 640  --height 400 \
  --text="ISO/RS02 data ($SIZE MB) \\n created at: $DATA_ISO"
# EOF

You may wish to create launcher on the desktop with command set something like "/usr/local/bin/gmkrs02 %d".

12.2. Make

Make is a utility to maintain groups of programs. Upon execution of make(1), make read the rule file, "Makefile", and updates a target if it depends on prerequisite files that have been modified since the target was last modified, or if the target does not exist. The execution of these updates may occur concurrently.

A regra de sintaxe do ficheiro é a seguinte.

target: [ prerequisites ... ]
 [TAB]  command1
 [TAB]  -command2 # ignore errors
 [TAB]  @command3 # suppress echoing

Here " [TAB] " is a TAB code. Each line is interpreted by the shell after make variable substitution. Use "\" at the end of a line to continue the script. Use "$$" to enter "$" for environment values for a shell script.

Implicit rules for the target and prerequisites can be written, for example, by the following.

%.o: %.c header.h

Here, the target contains the character "%" (exactly one of them). The "%" can match any nonempty substring in the actual target filenames. The prerequisites likewise use "%" to show how their names relate to the actual target name.

Tabela 12.10. Lista de variáveis automáticas do make

variável automática valor
$@ alvo
$< primeiro pre-requisito
$? todos os novos pre-requisitos
$^ todos os pre-requisitos
$* "%" matched stem in the target pattern

Tabela 12.11. Lista de expansões da variável do make

expansão da variável descrição
foo1 := bar expansão de uma vez
foo2 = bar expansão recursiva
foo3 += bar acrescentar

Run "make -p -f/dev/null" to see automatic internal rules.

12.3. C

You can set up proper environment to compile programs written in the C programming language by the following.

# apt-get install glibc-doc manpages-dev libc6-dev gcc build-essential

The libc6-dev package, i.e., GNU C Library, provides C standard library which is collection of header files and library routines used by the C programming language.

Veja referências para C nos seguintes.

  • "info libc" (Referência de funções da biblioteca C)
  • gcc(1) e "info gcc"
  • each_C_library_function_name(3)
  • Kernighan & Ritchie, "The C Programming Language", 2nd edition (Prentice Hall)

12.3.1. Programa C simples (gcc)

A simple example "example.c" can compiled with a library "libm" into an executable "run_example" by the following.

$ cat > example.c << EOF
#include <stdio.h>
#include <math.h>
#include <string.h>

int main(int argc, char **argv, char **envp){
        double x;
        char y[11];
        x=sqrt(argc+7.5);
        strncpy(y, argv[0], 10); /* prevent buffer overflow */
        y[10] = '\0'; /* fill to make sure string ends with '\0' */
        printf("%5i, %5.3f, %10s, %10s\n", argc, x, y, argv[1]);
        return 0;
}
EOF
$ gcc -Wall -g -o run_example example.c -lm
$ ./run_example
        1, 2.915, ./run_exam,     (null)
$ ./run_example 1234567890qwerty
        2, 3.082, ./run_exam, 1234567890qwerty

Here, "-lm" is needed to link library "/usr/lib/libm.so" from the libc6 package for sqrt(3). The actual library is in "/lib/" with filename "libm.so.6", which is a symlink to "libm-2.7.so".

Look at the last parameter in the output text. There are more than 10 characters even though "%10s" is specified.

The use of pointer memory operation functions without boundary checks, such as sprintf(3) and strcpy(3), is deprecated to prevent buffer overflow exploits that leverage the above overrun effects. Instead, use snprintf(3) and strncpy(3).

12.4. Depuração

Debug is important part of programing activities. Knowing how to debug programs makes you a good Debian user who can produce meaningful bug reports.

12.4.1. Execução gdb básica

O depurador principal em Debian é o gdb(1) que lhe permite inspeccionar um programa enquanto ele é executado.

Vamos instalar o gdb e programas relacionados com o seguinte.

# apt-get install gdb gdb-doc build-essential devscripts

Good tutorial of gdb is provided by "info gdb" or found elsewhere on the web. Here is a simple example of using gdb(1) on a "program" compiled with the "-g" option to produce debugging information.

$ gdb program
(gdb) b 1                # set break point at line 1
(gdb) run args           # run program with args
(gdb) next               # next line
...
(gdb) step               # step forward
...
(gdb) p parm             # print parm
...
(gdb) p parm=12          # set value to 12
...
(gdb) quit
[Dica] Dica

Many gdb(1) commands can be abbreviated. Tab expansion works as in the shell.

12.4.2. Depurar o pacote Debian

Since all installed binaries should be stripped on the Debian system by default, most debugging symbols are removed in the normal package. In order to debug Debian packages with gdb(1), corresponding *-dbg packages need to be installed (e.g. libc6-dbg in the case of libc6).

If a package to be debugged does not provide its *-dbg package, you need to install it after rebuilding it by the following.

$ mkdir /path/new ; cd /path/new
$ sudo apt-get update
$ sudo apt-get dist-upgrade
$ sudo apt-get install fakeroot devscripts build-essential
$ sudo apt-get build-dep source_package_name
$ apt-get source package_name
$ cd package_name*

Corrigir bugs se necessário

Bump package version to one which does not collide with official Debian versions, e.g. one appended with "+debug1" when recompiling existing package version, or one appended with "~pre1" when compiling unreleased package version by the following.

$ dch -i

Compile e instale pacotes com símbolos de depuração com o seguinte.

$ export DEB_BUILD_OPTIONS=nostrip,noopt
$ debuild
$ cd ..
$ sudo debi package_name*.changes

You need to check build scripts of the package and ensure to use "CFLAGS=-g -Wall" for compiling binaries.

12.4.3. Obtaining backtrace

When you encounter program crash, reporting bug report with cut-and-pasted backtrace information is a good idea.

The backtrace can be obtained by the following steps.

  • Correr o programa sob gdb(1).
  • Reproduzir o erro (crash).

    • It causes you to be dropped back to the gdb prompt.
  • Type "bt" at the gdb prompt.

In case of program freeze, you can crash the program by pressing Ctrl-C in the terminal running gdb to obtain gdb prompt.

[Dica] Dica

Often, you see a backtrace where one or more of the top lines are in "malloc()" or "g_malloc()". When this happens, chances are your backtrace isn't very useful. The easiest way to find some useful information is to set the environment variable "$MALLOC_CHECK_" to a value of 2 (malloc(3)). You can do this while running gdb by doing the following.

 $ MALLOC_CHECK_=2 gdb hello

12.4.4. Advanced gdb commands

Tabela 12.12. Lista de comandos gdb avançados

comando descrição dos objectivos do comando
(gdb) thread apply all bt get a backtrace for all threads for multi-threaded program
(gdb) bt full get parameters came on the stack of function calls
(gdb) thread apply all bt full get a backtrace and parameters as the combination of the preceding options
(gdb) thread apply all bt full 10 get a backtrace and parameters for top 10 calls to cut off irrelevant output
(gdb) set logging on write log of gdb output to a file (the default is "gdb.txt")

12.4.5. Depurar Erros do X

If a GNOME program preview1 has received an X error, you should see a message as follows.

O programa 'preview1' recebeu um erro do X Window System.

If this is the case, you can try running the program with "--sync", and break on the "gdk_x_error" function in order to obtain a backtrace.

12.4.6. Verificar a dependência em bibliotecas

Use ldd(1) to find out a program's dependency on libraries by the followings.

$ ldd /bin/ls
        librt.so.1 => /lib/librt.so.1 (0x4001e000)
        libc.so.6 => /lib/libc.so.6 (0x40030000)
        libpthread.so.0 => /lib/libpthread.so.0 (0x40153000)
        /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)

For ls(1) to work in a `chroot`ed environment, the above libraries must be available in your `chroot`ed environment.

See Secção 9.5.6, “Rastear as actividades de programas”.

12.4.7. Ferramentas de detecção de fugas de memória

Aqui estão várias ferramentas de detecção de fugas de memória em Debian.

Tabela 12.13. Lista de ferramentas de detecção de fugas de memória

pacote popcon tamanho descrição
libc6-dev * V:46, I:68 11292 mtrace(1): funcionalidades de depuração do malloc em glibc
valgrind * V:1.3, I:6 136416 depurador e perfilador de memória
kmtrace * V:0.3, I:2 324 Rastreador de fugas de memória do KDE que usa o mtrace(1) da glibc
alleyoop * V:0.05, I:0.3 596 Frontend do GNOME para o verificador de memória Valgrind
electric-fence * V:0.05, I:0.8 120 o depurador malloc(3)
leaktracer * V:0.01, I:0.11 116 rastreador de fugas de memória para programas C++
libdmalloc5 * V:0.01, I:0.2 356 biblioteca de depuração de alocação de memória
mpatrolc2 * V:0.00, I:0.01 3592 biblioteca para depurar alocações de memória

12.4.8. Ferramentas de análise de código estático

There are lint like tools for static code analysis.

Tabela 12.14. Lista de ferramentas para análise de código estático

pacote popcon tamanho descrição
splint * V:0.06, I:0.5 1836 ferramenta para verificação estática de programas C para bugs
rats * V:0.06, I:0.2 876 rough Auditing Tool for Security (C, C++, PHP, Perl, and Python code)
flawfinder * V:0.01, I:0.15 192 ferramenta para examinar código fonte C/C++ e procurar por fraquezas na segurança
perl * V:88, I:99 18528 interpreter with internal static code checker: B::Lint(3perl)
pylint * V:0.2, I:0.7 576 Verificador estático de código Python
jlint * V:0.01, I:0.09 156 Verificador de programa Java
weblint-perl * V:0.10, I:0.7 28 Verificado de sintaxe e estilo mínimo para HTML
linklint * V:0.05, I:0.3 432 fast link checker and web site maintenance tool
libxml2-utils * V:3, I:49 160 utilities with xmllint(1) to validate XML files

12.4.9. Disassemble binary

You can disassemble binary code with objdump(1) by the following.

$  objdump -m i386 -b binary -D /usr/lib/grub/x86_64-pc/stage1
[Nota] Nota

gdb(1) may be used to disassemble code interactively.

12.5. Flex — um Lex melhor.

Flex is a Lex-compatible fast lexical analyzer generator.

Tutorial for flex(1) can be found in "info flex".

You need to provide your own "main()" and "yywrap()". Otherwise, your flex program should look like this to compile without a library. This is because that "yywrap" is a macro and "%option main" turns on "%option noyywrap" implicitly.

%option main
%%
.|\n    ECHO ;
%%

Alternatively, you may compile with the "-lfl" linker option at the end of your cc(1) command line (like AT&T-Lex with "-ll"). No "%option" is needed in this case.

12.6. Bison — um Yacc melhor

Several packages provide a Yacc-compatible lookahead LR parser or LALR parser generator in Debian.

Tabela 12.15. List of Yacc-compatible LALR parser generators

pacote popcon tamanho descrição
bison * V:2, I:15 1504 GNU LALR parser generator
byacc * V:0.09, I:1.2 168 Berkeley LALR parser generator
btyacc * V:0.00, I:0.07 248 backtracking parser generator based on byacc

O tutorial para o bison(1) pode ser encontrado em "info bison".

You need to provide your own "main()" and "yyerror()". "main()" calls "yyparse()" which calls "yylex()", usually created with Flex.

%%

%%

12.7. Autoconf

Autoconf is a tool for producing shell scripts that automatically configure software source code packages to adapt to many kinds of Unix-like systems using the entire GNU build system.

autoconf(1) produces the configuration script "configure". "configure" automatically creates a customized "Makefile" using the "Makefile.in" template.

12.7.1. Compilar e instalar o programa

[Atenção] Atenção

Do not overwrite system files with your compiled programs when installing them.

Debian does not touch files in "/usr/local/" or "/opt". So if you compile a program from source, install it into "/usr/local/" so it does not interfere with Debian.

$ cd src
$ ./configure --prefix=/usr/local
$ make
$ make install # this puts the files in the system

12.7.2. Desinstalar o programa

If you have the original source and if it uses autoconf(1)/automake(1) and if you can remember how you configured it, execute as follows to uninstall the program.

$ ./configure "todas-as-opções-que-fornecer"
# make uninstall

Alternatively, if you are absolutely sure that the install process puts files only under "/usr/local/" and there is nothing important there, you can erase all its contents by the following.

# find /usr/local -type f -print0 | xargs -0 rm -f

If you are not sure where files are installed, you should consider using checkinstall(8) from the checkinstall package, which provides a clean path for the uninstall. It now supports to create a Debian package with "-D" option.

12.8. Perl short script madness

Although any AWK scripts can be automatically rewritten in Perl using a2p(1), one-liner AWK scripts are best converted to one-liner Perl scripts manually.

Let's think following AWK script snippet.

awk '($2=="1957") { print $3 }' |

Isto é equivalente a qualquer uma das seguintes linhas.

perl -ne '@f=split; if ($f[1] eq "1957") { print "$f[2]\n"}' |
perl -ne 'if ((@f=split)[1] eq "1957") { print "$f[2]\n"}' |
perl -ne '@f=split; print $f[2] if ( $f[1]==1957 )' |
perl -lane 'print $F[2] if $F[1] eq "1957"' |
perl -lane 'print$F[2]if$F[1]eq+1957' |

Este último é um enigma. Aproveitei-me das seguintes funcionalidades do Perl.

  • O espaço em branco é opcional.
  • A conversão automática existe de números para string.

See perlrun(1) for the command-line options. For more crazy Perl scripts, Perl Golf may be interesting.

12.9. Web

Basic interactive dynamic web pages can be made as follows.

  • Queries are presented to the browser user using HTML forms.
  • Filling and clicking on the form entries sends one of the following URL string with encoded parameters from the browser to the web server.

    • "http://www.foo.dom/cgi-bin/program.pl?VAR1=VAL1&VAR2=VAL2&VAR3=VAL3"
    • "http://www.foo.dom/cgi-bin/program.py?VAR1=VAL1&VAR2=VAL2&VAR3=VAL3"
    • "http://www.foo.dom/program.php?VAR1=VAL1&VAR2=VAL2&VAR3=VAL3"
  • "%nn" in URL is replaced with a character with hexadecimal nn value.
  • A variável de ambiente está definida como: "QUERY_STRING="VAR1=VAL1 VAR2=VAL2 VAR3=VAL3"".
  • CGI program (any one of "program.*") on the web server executes itself with the environment variable "$QUERY_STRING".
  • stdout of CGI program is sent to the web browser and is presented as an interactive dynamic web page.

For security reasons it is better not to hand craft new hacks for parsing CGI parameters. There are established modules for them in Perl and Python. PHP comes with these functionalities. When client data storage is needed, HTTP cookies are used. When client side data processing is needed, Javascript is frequently used.

For more, see the Common Gateway Interface, The Apache Software Foundation, and JavaScript.

Searching "CGI tutorial" on Google by typing encoded URL http://www.google.com/search?hl=en&ie=UTF-8&q=CGI+tutorial directly to the browser address is a good way to see the CGI script in action on the Google server.

12.10. A tradução do código fonte

Existem programas para converter códigos fonte.

Tabela 12.16. Lista de ferramentas de tradução de código fonte

pacote popcon tamanho palavra chave descrição
perl * V:88, I:99 18528 AWK→PERL convert source codes from AWK to PERL: a2p(1)
f2c * V:0.12, I:1.2 448 FORTRAN→C convert source codes from FORTRAN 77 to C/C++: f2c(1)
protoize * V:0.00, I:0.09 100 ANSI C Cria/remove protótipos ANSI de código C
intel2gas * V:0.01, I:0.07 344 intel→gas converter from NASM (Intel format) to the GNU Assembler (GAS)

12.11. Criando um pacote Debian

Se você deseja criar um pacote debian, leia o seguinte.

Existem pacotes como os dh-make, dh-make-perl, etc., que ajudam no processo em empacotamento.