Linux下的C程序如何调用系统命令，并获取系统的输出信息到C程序中

#include <stdio.h>    
#include <string.h>
#include <errno.h>

int main(int argc,char*argv[])
{
    FILE *fstream=NULL;
    char buff[1024];
    memset(buff,0,sizeof(buff));
    if(NULL==(fstream=popen("uname -a","r")))
    {
        fprintf(stderr,"execute command failed: %s",strerror(errno));
        return -1;
    }

    if(NULL!=fgets(buff, sizeof(buff), fstream))
    {
        printf("=>%s",buff);
    }   
    else
    {
        pclose(fstream);
        return -1;
    }
    pclose(fstream);
    return 0;
}

merlin@tfAnalysis:~/t/popen$ ./a.out 
=>Linux tfAnalysis 3.13.0-35-generic #62-Ubuntu SMP Fri Aug 15 01:58:01 UTC 2014 i686 i686 i686 GNU/Linux
merlin@tfAnalysis:~/t/popen$