当命令包含“..”时，系统 function 在 C 中不起作用

Question

This is my code:

#include<stdlib.h>
int main()
{
    system("getent passwd {1000..60000}");

    return 1;
}

I believe the ".." present in the command is causing the problem cause the program runs properly for other commands.

Answer 1

system does not run your normal shell. It instead always runs /bin/sh . From system (3) :

DESCRIPTION

The system () library function uses fork (2) to create a child process that executes the shell command specified in command using execl (3) as follows:

 execl("/bin/sh", "sh", "-c", command, (char *) NULL);

system() returns after the command has been completed.

Usually /bin/sh is a shell that does not understand {1000..60000} . To run bash or zsh you need to do something like

system("/bin/bash -c 'getent passwd {1000..60000}'");

Answer 2

Not an answer to your question about system(), but may be useful to you:

#include <pwd.h>
#include <stdio.h>
#include <sys/types.h>

int main() {
  struct passwd *p;
  while (NULL != (p = getpwent())) {
    printf("id=%d name=%s\n", p->pw_uid, p->pw_name);
  }
  endpwent();
  return 0;
}