PROGRAM – 1
Implementation of basic UNIX commands using file APIs
Write a program to implement commands ls( -l option), cp, rm and mv using UNIX file
APIs.
ls –l command
#include<stdio.h>
#include<dirent.h>
#include<sys/stat.h>
#include<pwd.h>
#include<grp.h>
#include<time.h>
int main()
{
DIR *d;
struct dirent *de;
struct stat buf;
int i,j;
char P[10]="rwxrwxrwx",AP[10]=" ";
struct passwd *p;
struct group *g;
struct tm *t;
char time[26];
d=opendir(".");
readdir(d);
readdir(d);
while( (de=readdir(d))!=NULL)
{
stat(de->d_name,&buf);
// File Type
if(S_ISDIR(buf.st_mode))
printf("d");
else if(S_ISREG(buf.st_mode))
printf("-");
else if(S_ISCHR(buf.st_mode))is it a character device file
printf("c");
else if(S_ISBLK(buf.st_mode))
printf("b");
else if(S_ISLNK(buf.st_mode))
printf("l");
else if(S_ISFIFO(buf.st_mode))
printf("p");
else if(S_ISSOCK(buf.st_mode))
printf("s");
//File Permissions P-Full Permissions AP-Actual Permissions
for(i=0,j=(1<<8);i<9;i++,j>>=1)
AP[i]= (buf.st_mode & j ) ? P[i] : '-' ;
printf("%s",AP);
//No. of Hard Links
printf("%5d",buf.st_nlink);
//User Name
p=getpwuid(buf.st_uid);
printf(" %.8s",p->pw_name);
//Group Name
g=getgrgid(buf.st_gid);
printf(" %-8.8s",g->gr_name);
//File Size
printf(" %8d",buf.st_size);
//Date and Time of modification
t=localtime(&buf.st_mtime);
strftime(time,sizeof(time),"%b %d %H:%M",t);
printf(" %s",time);
//File Name
printf(" %s\n",de->d_name);
}
}
cp command
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/types.h>
#include <unistd.h>
#define BUF_SIZE 8192
int main(int argc, char* argv[]) {
int input_fd, output_fd; /* Input and output file descriptors
*/
ssize_t ret_in, ret_out; /* Number of bytes returned by
read() and write() */
char buffer[BUF_SIZE]; /* Character buffer */
/* Are src and dest file name arguments missing */
if(argc != 3){
printf ("Usage: cp file1 file2");
return 1;
}
/* Create input file descriptor */
input_fd = open (argv [1], O_RDONLY);
if (input_fd == -1) {
perror ("open");
return 2;
}
/* Create output file descriptor */
output_fd = open(argv[2], O_WRONLY | O_CREAT, 0644);
if(output_fd == -1){
perror("open");
return 3;
}
/* Copy process */
while((ret_in = read (input_fd, &buffer, BUF_SIZE)) > 0){
ret_out = write (output_fd, &buffer, (ssize_t) ret_in);
if(ret_out != ret_in){
/* Write error */
perror("write");
return 4;
}
}
/* Close file descriptors */
close (input_fd);
close (output_fd);
return (EXIT_SUCCESS);
}
mv command
int main(int argc, char* argv[]) {
int input_fd, output_fd; /* Input and output file descriptors
*/
/* Are src and dest file name arguments missing */
if(argc != 3){
printf ("Usage: mv file1 file2");
return 1;
}
/* Create input file descriptor */
input_fd = link(argv [1], argv[2]);
if (input_fd == -1) {
perror ("link error");
return 2;
}
/* Create output file descriptor */
output_fd = unlink(argv[1]);
if(output_fd == -1){
perror("unlink");
return 3;
}
rm command
int main(int argc, char* argv[]) {
output_fd = unlink(argv[1]);
if(output_fd == -1){
perror("unlink error");
return 3;
}
}
$gcc -o myls ls.c
$./myls
$gcc -o mycp cp.c
$./mycp a.c b.c
$gcc -o mymv mv.c
$./mymv a.c b.c
$gcc -o myrm rm.c
$./myrm a.c
PROGRAM – 2
Process control system calls
Application to demonstrate use of fork, execve, wait, getpid, exit system calls.
AHost Program
#include<stdio.h>
#include<string.h>
#include<sys/types.h>
#include<stdlib.h>
#include<unistd.h>
#include<wait.h>
int main(int argc, char *argv[]){
printf("Main Function: \n");
int retval=1;
pid_t pid=fork();
if(pid<0){
printf("Error in fork operation\n");
}
if(pid==0){
printf("PID for Child process: %d\nPID of its parent process: %d\n",getpid(),getppid());
execl("./binsearch",argv[1],NULL);
}
else{
printf("PID of parent process: %d\n",getpid());
wait(&retval);
if(WIFEXITED(retval)==1)
{
printf("Child terminated normally\n");
}
else{
printf("Child terminated abnormally\n");
exit(0);
}
}
return 0;
}
Binary search application
#include<stdio.h>
int binarySearch(int arr[], int l, int r, int x)
{
if (r >= l) {
int mid = l + (r - l) / 2;
if (arr[mid] == x)
return 1;
if (arr[mid] > x)
return binarySearch(arr, l, mid - 1, x);
return binarySearch(arr, mid + 1, r, x);
}
return -1;
}
void swap(int *xp, int *yp) {
int temp = *xp;
*xp = *yp;
*yp = temp;
}
void sort(int arr[], int n) {
int i, j;
for (i = 0; i < n-1; i++)
for (j = 0; j < n-i-1; j++)
if (arr[j] > arr[j+1])
swap(&arr[j], &arr[j+1]);
}
int main(void){
int n,key, arr[10];
printf("Enter the number of elements in the array: ");
scanf("%d",&n);
printf("Enter the elements: ");
for(int i=0;i<n;i++)
scanf("%d",&arr[i]);
sort(arr,n);
printf("Enter element to be searched: ");
scanf("%d",&key);
int result = binarySearch(arr, 0, n - 1, key);
if(result==-1)
printf("Element is not present in array");
else
printf("Element is present");
return 0;
}
Output
