OS-(I) Assignment 2: Set C- 1)

Write a C program that behaves like a shell which displays the command prompt ‘myshell$’. It accepts the command, tokenize the command line and execute it by creating the child process.
Also implement the additional command ‘typeline’ as

myshell$ typeline n filename: It will display first n lines of the file.

myshell$ typeline -n filename: It will display last n lines of the file.

myshell$ typeline a filename: It will display all the lines of the file.

Solution:

#include<sys/types.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
void make_toks(char *s, char *tok[])
{
	int i=0;
	char *p;
	p = strtok(s," ");
	while(p!=NULL)
	{
		tok[i++]=p;
		p=strtok(NULL," ");
	}
	tok[i]=NULL;
}
void typeline(char *fn, char *op)
{
	int fh,i,j,n;
	char c;
	fh = open(fn,O_RDONLY);
	if(fh==-1)
	{
		printf("File %s not found.\n",fn);
		return;
	}
	if(strcmp(op,"a")==0)
	{
		while(read(fh,&c,1)>0)
			printf("%c",c);
		close(fh);
	return;
	}
	n = atoi(op);
	if(n>0)
	{
		i=0;
		while(read(fh,&c,1)>0)
		{
			printf("%c",c);
			if(c=='\n') 
				i++;
			if(i==n)
				break;
		}
	}
	if(n<0)
	{
		i=0;
		while(read(fh,&c,1)>0)
		{

			if(c=='\n') 
				i++;
		}
		i++;
		lseek(fh,0,SEEK_SET);
		j=0;
		while(read(fh,&c,1)>0)
		{
			if(c=='\n')
				j++;
			if(j==i+n) 
				break;
		}
		while(read(fh,&c,1)>0)
		{
			printf("%c",c);
		}
		printf("\n");
	}
	close(fh);
}
int main()
{
	char buff[80],*args[10];
	int pid;
	while(1)
	{
		printf("myshell$");
		fflush(stdin);
		fgets(buff,80,stdin);
		buff[strlen(buff)-1]='\0';
		make_toks(buff,args);
		if(strcmp(args[0],"typeline")==0)
			typeline(args[2],args[1]);
		else if(strcmp(args[0],"exit")==0)
			exit(0);
		else
		{
			pid = fork();
			if(pid>0)
				wait(NULL);
			else
			{
				if(execvp(args[0],args)==-1)
				printf("Bad command.\n");
			}
		}
	}
	return 0;
}