How do I get system answer in c

Applications Programming
1

How do I get the answer of a system call that is printed in the terminal?

for example:

I execute system("pwd");
and get the answer /home/user/

But because I need to send this result to somewhere, I need to store it in a string.

Thanks in advance.

2

Use popen() instead.

3

Instead of what?
I do not create or open a file. All I need is to get the answer of any command from the command line into a string, "pwd" is just an example.

Can you please give a simple example?

Situation: I have

char command[50] = "ls";

system(command); // executes the string

___________________?

4

you can use popen following way:

#include <stdio.h>
int main()
{
#define BUFSIZE 1024
char buf[1024];
FILE *fp = NULL;
char *cmd = "ls -al /home/";
int nbytes = 0;
int fbytes = BUFSIZE;
int ch =0;
fp = popen(cmd, "r");
if (fp == NULL)  {
        printf("unable to open %s", cmd);
        exit(0);
}

while (nbytes < fbytes && (ch = fgetc(fp)) != EOF)
        buf[nbytes++] = ch;
buf[nbytes] = 0;
pclose(fp);
printf("output for %s %d:\n %s", cmd , nbytes, buf);
return 0;
}
5

thanks for answering

6

it works for some commands for example pwd, ifconfig, netstat, etc; but it does not get some answers such as "No such file or directory" when I used "gcc nonExistent.c" or "route help".
Any ideas?

7

netstat, ifconfig are not in your PATH. Try with providing full path or Might be you need supreuser permissions.
First try these commands on your promopt/shell.

8

Actually the problem is that you are getting those messages on standard error, not standard output. Try popen3 if your system has that.