A simple simulation of shell in Linux for learning. A blog (in Chinese) of introduction and how to build it :http://www.cnblogs.com/wuyuegb2312/p/3399566.html
type
make wshell
for wshell read input by fgets() or
make wshell_r
for wshell with readline lib.It need to install libreadline5-dev first.
Because of the lack of support for regular expressions , typing file's names such as "*.c" are not support.
main program
print out the prompt of wshell including path,hostname
read command input, and analyse the command and parameter(s).
support some built-in command,such as exit,quit,about, and cd.
a test program, helloworld, which can be executed in wshell.
analyses user's input line and tell them to wshell.
-Make the README.md be a real markdown file.
-Bug fix1:
Redirection operator ">>" will append a file, not trunc it to 0-size.
As noted by caiminfeng .
-Bug fix2:
When inputed "cd", it would be core dump before.
As noted by guokesong in issues2.
-Bug fix:
In readline mode, the spaces alloced by readline() was freed only once.Now they are all freed in the end of read_command().
As noted by xingfe123
-Bug fix:
Add handler of SIGCHLD. Earlier wshell would ignore the zombie process in background.
The handler only process the background process whose pid are saved in a array.
-Adjust some indents, although they are not errors.
-Bug fix:
Output redirect function was not completed. '>' still is for make new file,but '>>' append to any file now.
-Implemented a simple parsing function parse() to analyses the user input.
-Support I/O redirect, background running, and pipe.
-Bug fix:
Typing ctrl+d will normal exit wshell. before, segment fault when using readline lib.
Lack of free() somewhere, which may lead to memory leak.
-Implemented some builtin command,such as exit/quit, about, and, cd.
-Bug fix:
Never free the memory of command and parameters before, which may cause memory leak.
To solve it, read_command() has been rewrited, and is more like the one in Linux.
-Rewrite read_command():
There is no need to malloc for command and parameters any more.
All these just are pointers now.
-Supply two versions:
Using readline lib and not.the former need installing readline lib.
Type "make wshell_r" to make the former,and "make wshell" for another.
-Use execvp() instead of execve() to handle with commands like ls.
-Detect whether the shell is executed as root by geteuid()
-Bug fix:
execv()'s arg[0] usually is the name of command without path.
earlier version is not correct.
-Plan to do:
a built-in cd command.
##10.16 -A shell with basic function: get input and execute the test program(hello world).
为了学习而编写的Linux下shell的简单模拟实现。 介绍如何一步一步编写该程序的博客：http://www.cnblogs.com/wuyuegb2312/p/3399566.html
输入
make wshell
构建使用fgets()接收命令的wshell
make wshell_r
构建使用readline接收命令的wshell。需要安装libreadline5-dev或其他类似的库。
由于不支持正则表达式，含有通配符如"*.c"这样的文件名是不支持的。 不存在的命令不会提示。
主程序
拼接当前路径、主机名的提示符。
读取输入的命令，并分离出其中的参数。
提供对基本内建命令的支持，含exit、quit、about、cd等。
用来在wshell中执行的测试程序。
分析用户输入（是否使用了管道、重定向、后台执行等）。
-让README.md成为了真正的markdown文件
-调整部分缩进
-Bug修复1:
重定向符">>"将正确地在文件存在时做追加，而非把它变成0大小的文件。
感谢caiminfeng 的指出。
-Bug修复2:
当输入不带参数的 `cd`时，会导致崩溃。
-Bug修复:
在readline模式下, readline()申请的内存不会被释放。
感谢xingfe123 指出。
-Bug修复:
增加了SIGCHLD信号的处理器。较早版本的wshell不会处理后台的僵尸进程。
但是该处理器只会处理事先保存了pid的子进程。
-调整了不会导致错误的缩进。
-Bug修复:
输出重定向尚未完成。 '>' 仍然会创建新文件，但是'>>'会往文件末尾追加。
-实现了用于分析用户输入的函数parse()。
-支持输入输出重定向、管道、后台运行。
-Bug修复:
输入ctrl+d会正常退出wshell了。此前，在使用readline库时会段错误。
由于某处缺少free(), 会内存泄漏。
-实现了一些内建命令，包括`exit` 、 `quit` 、 `about` 、 `cd`。
-Bug修复:
从未释放命令和参数的空间，导致内存泄漏。
重写read_command()以解决这个问题，现在的行为更像Linux的了。
-重写read_command():
现在没必要为command和parameter释放内存了，它们只是指针。
-提供了两个版本:
使用readline库和不使用的。前者需要事先安装这个库。
输入"make wshell_r"可以生成前者，而"make wshell"会生成后者。
-用execvp()代替execve()处理 `ls` 这种命令。
-通过geteuid()判断shell是否执行在root用户下。
-Bug修复:
execv()'的arg[0]一般是不含路径的命令，上一个版本处理有误。
-下一步计划:
支持内建命令 `cd`。
##10.16 -一个具有基本功能的shell: 获取输入并执行测试程序(hello world).
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