第 12 章 编程

目录

12.1. Shell 脚本
12.1.1. POSIX shell 兼容性
12.1.2. Shell 参数
12.1.3. Shell conditionals
12.1.4. shell 循环
12.1.5. shell 命令行的处理顺序
12.1.6. 用于 shell 脚本的应用程序
12.1.7. shell 脚本对话框
12.1.8. Shell script example with zenity
12.2. Make
12.3. C
12.3.1. Simple C program (gcc)
12.4. Debug
12.4.1. Basic gdb execution
12.4.2. Debugging the Debian package
12.4.3. Obtaining backtrace
12.4.4. Advanced gdb commands
12.4.5. Debugging X Errors
12.4.6. Check dependency on libraries
12.4.7. Memory leak detection tools
12.4.8. Static code analysis tools
12.4.9. Disassemble binary
12.5. Flex — a better Lex
12.6. Bison — a better Yacc
12.7. Autoconf
12.7.1. Compile and install a program
12.7.2. Uninstall program
12.8. Perl short script madness
12.9. Web
12.10. 源代码转换
12.11. 制作 Debian 包

这里我给出一些 Debian 系统中的信息,帮助学习编程的人找出打包的源代码。下面是值得关注的软件包和与之对应的文档。

表 12.1. 帮助编程的软件包清单

软件包 流行度 大小
autoconf V:25, I:221 1868 autoconf-doc 包提供的“info autoconf
automake V:23, I:213 1707 automake1.10-doc 包提供的“info automake
bash V:859, I:999 5786 bash-doc 包提供的“info bash
bison V:11, I:114 2051 bison-doc 包提供的“info bison
cpp V:407, I:815 41 cpp-doc 包提供的“info cpp
ddd V:1, I:13 3692 ddd-doc 包提供的“info ddd
exuberant-ctags V:7, I:37 333 exuberant-ctags(1)
flex V:10, I:101 1077 flex-doc 包提供的“info flex
gawk V:352, I:468 2029 gawk-doc 包提供的“info gawk
gcc V:163, I:611 41 gcc-doc 包提供的“info gcc
gdb V:23, I:142 7307 gdb-doc 包提供的“info gdb
gettext V:53, I:371 7035 gettext-doc 包提供的“info gettext
gfortran V:22, I:62 16 gfortran-doc 包提供的“info gfortran”(Fortran 95)
fpc I:4 113 fpc(1) 和由 fp-docs 包提供的 html 文档(Pascal)
glade V:1, I:12 2212 通过 UI Builder 菜单提供的文档
libc6 V:927, I:998 10670 通过 glibc-docglibc-doc-reference 提供的“info libc
make V:164, I:626 1195 通过 make-doc 包提供的“info make
xutils-dev V:2, I:19 1465 imake(1)xmkmf(1) 等。
mawk V:402, I:997 198 mawk(1)
perl V:617, I:995 674 perl(1) 以及通过 perl-docperl-doc-html 提供的 html 文档
python V:674, I:988 647 python(1) 以及通过 python-doc 包提供的 html 文档
tcl8.4 V:4, I:66 184 tcl(3) 以及通过 tcl8.4-doc 包提供的更详细的手册页文档
tk8.4 V:2, I:42 185 tk(3) 以及通过 tk8.4-doc 包提供的更详细的手册页文档
ruby V:87, I:316 37 ruby(1) 以及通过 ri 包提供的交互式参考手册
vim V:127, I:390 2366 通过 vim-doc 包提供的帮助(F1)菜单
susv2 I:0 15 通过“单一UNIX规范(版本2)”获取(英语文档)
susv3 I:0 15 通过“单一UNIX规范(版本3)”获取(英语文档)

安装 manpagesmanpages-dev 包之后,可以通过运行“man 名称”查看手册页中的参考信息。安装了 GNU 工具的相关文档包之后,可以通过运行“info 程序名称”查看参考文档。某些 GFDL 协议的文档与 DFSG 并不兼容,所以你可能需要在 main 仓库中包含 contribnon-free 才能下载并安装它们。

[警告] 警告

不要用“test”作为可执行的测试文件的名字,因为 shell 中内建有“test”命令。

[小心] 小心

你可以把从源代码编译得到的程序直接放到“/usr/local”或“/opt”目录,这样可以避免与系统程序撞车。

[提示] 提示

“歌曲:99瓶啤酒”的代码示例可以给你提供实践各种语言的好范本。

Shell 脚本 是指包含有下面格式的可执行的文本文件。

#!/bin/sh
…… 命令

第一行指明了读取并执行这个文件的 shell 解释器。

读懂 shell 脚本的最好 办法是先理解类 UNIX 系统是如何工作的。这里有一些 shell 编程的提示。看看“Shell 错误”(http://www.greenend.org.uk/rjk/2001/04/shell.html),可以从错误中学习。

不像 shell 交互模式(参见第 1.5 节 “简单 shell 命令”第 1.6 节 “类 Unix 的文本处理”),shell 脚本会频繁使用参数、条件和循环等。

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

  • Success: 0 ("True")

  • Error: non 0 ("False")

[注意] 注意

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

[注意] 注意

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

Basic conditional idioms to remember are the following.

  • "<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.



算术整数的比较在条件表达式中为 "-eq","-ne","-lt","-le","-gt" 和 "-ge"。

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".

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.

The rule file syntax is the following.

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.



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

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.

See references for C as the following.

  • "info libc" (C library function reference)

  • gcc(1) and "info gcc"

  • each_C_library_function_name(3)

  • Kernighan & Ritchie, "The C Programming Language", 2nd edition (Prentice Hall)

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

Primary debugger on Debian is gdb(1) which enables you to inspect a program while it executes.

Let's install gdb and related programs by the following.

# 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
[提示] 提示

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

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.

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


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

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

%%

%%

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.

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 }' |

This is equivalent to any one of the following lines.

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' |

The last one is a riddle. It took advantage of following Perl features.

  • The whitespace is optional.

  • The automatic conversion exists from number to the string.

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

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.

  • The environment variable is set as: "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.

更多信息,参见 通用网关接口, Apache 软件基金会, 和 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.

源代码转换程序。


如果你想制作一个 Debian 包,阅读下面内容。

debmake, dh-make, dh-make-perl 等软件包,对软件包打包过程,也有帮助。