用C编写自己的shell，如何运行Unix可执行文件? [英] Writing my own shell in C, how do I run Unix executables?

问题描述

在我的一门课程中，我们正在编写自己的shell(基本上从头开始).

In one of my courses we're writing our own shell (basically from scratch).

我们已经处理过编写词法分析器和解析器，以将输入分为易于处理的漂亮命令"结构.同样，我有一个函数read_command()，它可以一次读取一个命令，并弄清它是什么类型的命令(管道/和/或/简单/等).

We've already handled writing a lexer and a parser to divide the input into nice "command" structures that are easier to deal with. Likewise, I have a function read_command() that will read one command in at a time and figure out what type of command it is (pipe/and/or/simple/etc.).

我现在正在尝试编写execute_command(struct command cmd)函数，该函数实际上接受命令并运行它.我正在为如何开始实际编写此功能而苦苦挣扎.

I now am trying to write the execute_command(struct command cmd) function that actually takes the command and runs it. I'm struggling on how to even start actually writing this function.

比方说，我只是得到一个非常简单的cat foo.txt作为命令.我的命令结构会将它整齐地分割，所以我有一个包含两个单词的单词数组.

Let's say I just get a very simple cat foo.txt as the command. My command structure will divide it up neatly so I have a word array with both words in it.

现在，我要使用参数foo.txt运行cat可执行文件.我意识到我应该使用$PATH变量来尝试找到可执行文件，然后使用此参数运行它.

Now I want to run the cat executable with the argument foo.txt. I realize I should use the $PATH variable to try to find the executable and then run it with this argument.

我正在努力解决几个主要问题:

I'm struggling with a few major questions:

1. 我实际上如何搜索命令cat?请记住，该程序使用C.我可以使用哪些功能搜索目录?如何使用PATH来做到这一点?
2. 找到命令cat后，如何使用foo.txt作为参数运行它?如何在C语言中完成此操作?

1. How do I actually search for the command cat? Keep in mind this program uses C. What functions can I use to search through directories? How do I use PATH to do this?
2. When I do find the command cat, how can I run it with foo.txt as a parameter? How can this be done in C?

推荐答案

1. 查看 getenv(3) 及其亲戚.您实际上可能实际上不需要直接对目录执行任何操作，但是如果这样做，则可以使用 opendir(3) ， readdir(3) ， fork(2) 和 execve(2) 是基本级别的API).

手册页本身或通过简单的google搜索这些功能中的任何一个，都会提供大量示例来帮助您.

The man pages themselves or a simple google search for any of these functions will turn up plenty of examples to help you along.

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