In this assignment, you are to write a C program – let\'s call it myls.c – that
ID: 3683207 • Letter: I
Question
In this assignment, you are to write a C program – let's call it myls.c – that mimics the ls command. Your program should implement the following ls options:
1. ls with no option: list the names of files and directories in the current directory
2. ls -i option: list the names and i-node numbers of files and directories in the current directory
3. ls -l option: list the names of files and directories in long format
4. ls -R option: recursively list the names of all files and directories in the current directory; that is, the command is also applied to the directories within the current directory, the directories within those directories, and so forth
Your program should not use fork/exec, but instead use the actual file system calls themselves:
• opendir() – open a directory
• readdir() – read a directory entry
• closedir() – close a directory
• rewinddir() – reset directory
• getcwd() – get current working directory
• chdir – change current working directory
• stat(), lstat(), fstat() – obtain file information
Explanation / Answer
I have written a c code for the same:
#include <sys/types.h>
#include <sys/dir.h>
#include <sys/param.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <dirent.h>
#include <pwd.h>
#include <grp.h>
#include <time.h>
#include <locale.h>
#include <langinfo.h>
#include <stdint.h>
#include <fcntl.h>
static char perms_buff[30];
const char *get_options(mode_t mode)
{
char ftype = '?';
if (S_ISREG(mode)) ftype = '-';
if (S_ISLNK(mode)) ftype = 'l';
if (S_ISDIR(mode)) ftype = 'd';
if (S_ISBLK(mode)) ftype = 'b';
if (S_ISCHR(mode)) ftype = 'c';
if (S_ISFIFO(mode)) ftype = '|';
sprintf(perms_buff, "%c%c%c%c%c%c%c%c%c%c %c%c%c", ftype,
mode & S_IRUSR ? 'r' : '-',
mode & S_IWUSR ? 'w' : '-',
mode & S_IXUSR ? 'x' : '-',
mode & S_IRGRP ? 'r' : '-',
mode & S_IWGRP ? 'w' : '-',
mode & S_IXGRP ? 'x' : '-',
mode & S_IROTH ? 'r' : '-',
mode & S_IWOTH ? 'w' : '-',
mode & S_IXOTH ? 'x' : '-',
mode & S_ISUID ? 'U' : '-',
mode & S_ISGID ? 'G' : '-',
mode & S_ISVTX ? 'S' : '-');
return (const char *)perms_buff;
}
char pathname[MAXPATHLEN];
void die(char *msg)
{
perror(msg);
exit(0);
}
static int
one (const struct dirent *unused)
{
return 1;
}
int main()
{
int count,i;
struct direct **files;
struct stat statbuf;
char datestring[256];
struct passwd pwent;
struct passwd *pwentp;
struct group grp;
struct group *grpt;
struct tm time;
char buf[1024];
if(!getcwd(pathname, sizeof(pathname)))
die("Error getting pathnamen");
count = scandir(pathname, &files, one, alphasort);
if(count > 0)
{
printf("total %d ",count);
for (i=0; i<count; ++i)
{
if (stat(files[i]->d_name, &statbuf) == 0)
{
printf("%10.10s", get_options(statbuf.st_mode));
printf(" %d", statbuf.st_nlink);
if (!getpwuid_r(statbuf.st_uid, &pwent, buf, sizeof(buf), &pwentp))
printf(" %s", pwent.pw_name);
else
printf(" %d", statbuf.st_uid);
if (!getgrgid_r (statbuf.st_gid, &grp, buf, sizeof(buf), &grpt))
printf(" %s", grp.gr_name);
else
printf(" %d", statbuf.st_gid);
printf(" %5d", (int)statbuf.st_size);
localtime_r(&statbuf.st_mtime, &time);
strftime(datestring, sizeof(datestring), "%F %T", &time);
printf(" %s %s ", datestring, files[i]->d_name);
}
free (files[i]);
}
free(files);
}
}