head.c

#include "types.h"
#include "stat.h"
#include "user.h"

char buf[512];

void
head(int fd, char *name, int line)
{
    int i, n; //here the size of the read chunk is defined by n, and i is used to keep a track of the chunk index
    int l, c; // here line number is defined by l, and the character count in the string is defined by c

    l = c = 0;

  while((n = read(fd, buf, sizeof(buf))) > 0 )
  {
    for(i=0;i<=n ;i++)
    {				//print the characters in the line 
      if(buf[i]!='\n'){			
      	printf(1,"%c",buf[i]);
      }	
				//if the number of lines is equal to l, then exit
      else if (l == (line-1)){
	printf(1,"\n");	
	exit();
      }
				//if the number of lines is not equal to l, then jump to next line and increment the value of l 
      else{
      	printf(1,"\n");
      	l++;
      } 
    }
  }

  if(n < 0){
    printf(1, "head: read error\n");
    exit();
  }
}



int 
main(int argc, char *argv[]) {
      int i;
      int fd = 0;	// when the file is not specified, then it will take input from the user
      int x = 10;	// will read the first 10 lines by default
      char *file;	// pointer to the name of the file
      char a;

      file = ""; // in the case when no file name is specified, it will take input from the user

      if (argc <= 1) {	
            head(0, "", 10);	// handles the default case of taking input from user for 10 lines
            exit();
      }

      else {
            for (i = 1; i < argc; i++) {
		a = *argv[i];	// assigns the char value of the argv to the var a
				
                  if (a == '-') { // it means that -NUM is provided, hence limited number of lines are to be printed
			argv[i]++;
                        x = atoi(argv[i]++);
                  }
				
                  else {	// if a !='-' then it implies that number of lines are not defined and hence default lines will print
			if ((fd = open(argv[i], 0)) < 0) {// this will execute if the file is unable to open
                        printf(1, "head: cannot open %s\n", argv[i]);
                        exit();
                        }
                  }
            }
		 
            head(fd, file, x);
            close(fd);
            exit();    

      }
}