在Unix环境中，有没有办法以编程方式在C中调用哪个？

For a project in C, we need to build a shell over a Unix server.

对于C语言中的项目,我们需要在Unix服务器上构建一个shell。

It needs to be able to execute functionality native to Unix, and not bash (or any other Unix shell).

它需要能够执行Unix本机的功能,而不是bash(或任何其他Unix shell)。

I am writing a method in the hopes to generalize a call to a command. into a general function:

我正在编写一种方法,希望能够概括对命令的调用。进入一般功能:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <string.h>
#include <limits.h>

void execCmd(char* cmd,char* options)
{
   char directory[MAX_CANON] = "/bin/"; //currently is just set to /bin
   char* toExec = strcat(directory,cmd);

I would like to set the variable 'directory' to the proper directory for the Unix command I'm calling.

我想将变量'directory'设置为我正在调用的Unix命令的正确目录。

So, in essence, I would like to be able to use something like char directory[MAX_CANON] = which(cmd);

所以,从本质上讲,我希望能够使用类似char目录[MAX_CANON] = which(cmd);

so that the which function will return me the directory of the command I'm trying to call.

以便哪个函数将返回我正在尝试调用的命令的目录。

If you feel this is not a good solution, please recommend some other way.

如果您认为这不是一个好的解决方案,请推荐其他方式。

Thanks

EDIT: I guess at worst I could do a massive if-else statement, setting the 'directory' vbl based on the cmd parameter.

编辑:我想最糟糕的是我可以做一个巨大的if-else语句,根据cmd参数设置'目录'vbl。

3 个解决方案

#1

What you're asking for is the command 'which', ie

你要求的是命令'which',即

me@*:~$ which which
/usr/bin/which

On linux it's a shell script, so take a look a gander.

在linux上它是一个shell脚本,所以看一看。

However, I don't think this is required to make a UNIX shell. If you type

但是,我不认为这是制作UNIX shell所必需的。如果你输入

man 3 exec

you'll find that execlp() and execvp() take care of the details of searching PATH for the given command and executing it.

你会发现execlp()和execvp()负责处理搜索给定命令的PATH并执行它的细节。

#2

To implement this natively, I would:

为了实现这一点,我会:

Use getenv to acquire the PATH

使用getenv获取PATH

parse the PATH into a list of candidate components (strtok for all its faults is the classic tool),

将PATH解析为候选组件列表(strtok的所有错误是经典工具),

For each PATH component: form /possible/path/to/cmd and use a stat family function to test fif this file exists and the user has execute permission. Continue until you find it or run out of PATH...

对于每个PATH组件:form / possible / path / to / cmd并使用stat系列函数来测试该文件是否存在,并且用户具有执行权限。继续,直到找到它或用完PATH ...

Edit: You may want to follow symlinks, too.

编辑:您可能也想要遵循符号链接。

#3

Not that I'm aware off, but you can mimic the which functionality on a helper function. I'll need to search over all paths in the PATH environment variable for a file named as your command, and after that check if that file is executable, then you probably found your executable.

不是我知道,但你可以模仿辅助函数的功能。我需要在PATH环境变量中的所有路径上搜索一个名为命令的文件,然后检查该文件是否可执行,那么您可能找到了可执行文件。

To get the PATH variable you can use getenv(). You'll need to split it with strtok(). For searching a directory you can use opendir(), will be something like this:

要获取PATH变量,可以使用getenv()。你需要用strtok()拆分它。要搜索目录,您可以使用opendir(),将是这样的:

#include <sys/types.h>
#include <dirent.h>

...
    DIR *dir;
    struct dirent *dp;
...
    if ((dir = opendir (".")) == NULL) {
        perror ("Cannot open .");
        exit (1);
    }


    while ((dp = readdir (dir)) != NULL) {
    }
...

Check for dirent struct on the readdir() function man page.

检查readdir()函数手册页中的dirent结构。

#1