free_disk_space.c

// Free disk space using statvfs() and df -h.

#include <stdio.h>
#include <stdlib.h>
#include <sys/statvfs.h>

float _statvfs()
{
  int err;
  struct statvfs stat;

  if ((statvfs("/", &stat)) < 0 )
  {
    printf("failed to stat!\n");
    exit(1);
  }

  return (stat.f_bavail * stat.f_bsize) / 1024 / 1024 / 1024;
}

char * _system(const char *cmd, char *buf)
{
  FILE *f;
  f = popen(cmd, "r");
  if (!f)
  {
    printf("failed to open pipe!\n");
    exit(1);
  }

  fgets(buf, 10, f);
  pclose(f);
  return buf;
}

void main()
{
  char buf[10];

  printf("statvfs() : %.2fG\n", _statvfs());
  printf("df -f     : %s",
         _system("df -h / | tail -1 | awk '{print $4}'", buf));
}