unix command result to a variable - char*

How can I assign "pwd" (or any other command in that case) result (present working dir) to a variable which is char*?

command can be anything. Not bounded to ju开发者_如何学运维st "pwd".

Thanks.

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Start with popen. That will let you run a command with its standard output directed to a FILE * that your parent can read. From there it's just a matter of reading its output like you would any normal file (e.g., with fgets, getchar, etc.)

Generally, however, you'd prefer to avoid running an external program for that -- you should have getcwd available, which will give the same result much more directly.

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Why not just call getcwd()? It's not part of C's standard library, but it is POSIX, and it's very widely supported.

Anyway, if pwd was just an example, have a look at popen(). That will run an external command and give you a FILE* with which to read its output.

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There is a POSIX function, getcwd() for this - I'd use that.

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#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

int main(int argc, char* argv[]) {
    char *dir;
    dir = getcwd(NULL, 0);
    printf("Current directory is: %s\n", dir);
    free(dir);
    return 0;
}

I'm lazy, and like the NULL, 0 parameters, which is a GNU extension to allocate as large a buffer as necessary to hold the full pathname. (It can probably still fail, if you're buried a few hundred thousand characters deep.)

Because it is allocated for you, you need to free(3) it when you're done. I'm done with it quickly, so I free(3) it quickly, but that might not be how you need to use it.

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You can fork and use one of the execv* functions to call pwd from your C program, but getting the result of that would be messy at best.

The proper way to get the current working directory in a C program is to call char* getcwd(char* name, size_t size);