read-line.c

/*
 * CS354: Operating Systems. 
 * Purdue University
 * Example that shows how to read one line with simple editing
 * using raw terminal.
 */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#define MAX_BUFFER_LINE 2048

extern void tty_raw_mode(void);

// Buffer where line is stored
int line_length;
char line_buffer[MAX_BUFFER_LINE];

// Simple history array
// This history does not change. 
// Yours have to be updated.
int history_index = 0;
char * history [128];
int history_length = 0;

void read_line_print_usage()
{
  char * usage = "\n"
    " ctrl-?       Print usage\n"
    " Backspace    Deletes last character\n"
    " up arrow     See last command in the history\n";

  write(1, usage, strlen(usage));
}

/* 
 * Input a line with some basic editing.
 */
char * read_line() {

  // Set terminal in raw mode
  tty_raw_mode();

  line_length = 0;
  int line_loc = line_length;

  // Read one line until enter is typed
  while (1) {

    // Read one character in raw mode.
    char ch;
    read(0, &ch, 1);

    if (ch>=32) {
      // It is a printable character. 

		//backspace
		if (ch == 127){
			if(line_length > 0){
				ch = 8;
				write(1,&ch,1);
				// Write a space to erase the last character read
				ch = ' ';
				write(1,&ch,1);

				// Go back one character
				ch = 8;
				write(1,&ch,1);
				// Remove one character from buffer
				line_length--;
				line_loc--;
			}
			continue;
		}

		// Do echo
		write(1,&ch,1);

		// If max number of character reached return.
		if (line_length==MAX_BUFFER_LINE-2) 
			break; 

		// add char to buffer.
		line_buffer[line_length]=ch;
		if(line_loc == line_length)
			line_length++;
		line_loc++;
    }
    else if (ch==10) {
      // <Enter> was typed. Return line
      
      // Print newline
      write(1,&ch,1);

      break;
    }
    else if (ch == 31) {
      // ctrl-?
      read_line_print_usage();
      line_buffer[0]=0;
      break;
    }
    else if (ch == 8) {
      // <backspace> was typed. Remove previous character read.

      // Go back one character
      	ch = 8;
      	write(1,&ch,1);

      // Write a space to erase the last character read
      	ch = ' ';
      	write(1,&ch,1);

      // Go back one character
      	ch = 8;
      	write(1,&ch,1);

      // Remove one character from buffer
      	line_length--;
	line_loc--;
    }
    else if (ch==27) {
      // Escape sequence. Read two chars more
      //
      // HINT: Use the program "keyboard-example" to
      // see the ascii code for the different chars typed.
      //
      char ch1; 
      char ch2;
      read(0, &ch1, 1);
      read(0, &ch2, 1);
      if (ch1==91 && ch2==65) {
	// Up arrow. Print next line in history.
	

	// Erase old line
	// Print backspaces
	int i = 0;
	for (i =0; i < line_length; i++) {
	  ch = 8;
	  write(1,&ch,1);
	}

	// Print spaces on top
	for (i =0; i < line_length; i++) {
	  ch = ' ';
	  write(1,&ch,1);
	}

	// Print backspaces
	for (i =0; i < line_length; i++) {
	  ch = 8;
	  write(1,&ch,1);
	}	

	// Copy line from history
	if(history_length > 0 && history_index >= 0){
		strcpy(line_buffer, history[history_index--]);
		history_index=(history_index)%history_length;
		if(history_index == -1){
			history_index = history_length - 1;
		}

		line_length = strlen(line_buffer);
	}
	// echo line
	write(1, line_buffer, line_length);
      }// end of up
      else if (ch1==91 && ch2==66) {
	// Down arrow. Print prev line in history.

	// Erase old line
	// Print backspaces
	int i = 0;
	for (i =0; i < line_length; i++) {
	  ch = 8;
	  write(1,&ch,1);
	}

	// Print spaces on top
	for (i =0; i < line_length; i++) {
	  ch = ' ';
	  write(1,&ch,1);
	}

	// Print backspaces
	for (i =0; i < line_length; i++) {
	  ch = 8;
	  write(1,&ch,1);
	}	

	// Copy line from history
	if(history_length > 0 && history_index <= history_length-1)
		strcpy(line_buffer, history[history_index++]);
	else if(history_index == history_length){
		history_index = history_length - 1;
		strcpy(line_buffer,"");
	}

	line_length = strlen(line_buffer);
	// echo line
	write(1, line_buffer, line_length);
	}//End down arrow	      
	else if (ch1==91 && ch2==68) {
	     	//Left Arrow
		if(line_loc > 0){
			ch = 27;
			write(1,&ch,1);
			ch = 91;
			write(1,&ch,1);
			ch = 68;
			write(1,&ch,1);
			line_loc--;		
		}
	  }//End Left
	 else if (ch1==91 && ch2==67) {
		 //Right Arrow
		if(line_loc < line_length){
			ch = 27;
			write(1,&ch,1);
			ch = 91;
			write(1,&ch,1);
			ch = 67;
			write(1,&ch,1);
			line_loc++;			
			}
		 }//End Right
	  else if (ch1==79 && ch2==72){ //Home
		while(line_loc > 0){
			ch = 27;
			write(1,&ch,1);
			ch = 91;
			write(1,&ch,1);
			ch = 68;
			write(1,&ch,1);
			line_loc--;		
		}
	  } //End Home

	else if (ch1==79 && ch2==70){ //End
		while(line_loc != line_length){
			ch = 27;
			write(1,&ch,1);
			ch = 91;
			write(1,&ch,1);
			ch = 67;
			write(1,&ch,1);
			line_loc++;			
		}
	  } //End End 
    }

  }

  // Add eol and null char at the end of string
  line_buffer[line_length]=10;
  line_length++;
  line_buffer[line_length]=0;

  //update history
  	history[history_length] = (char *)malloc(strlen(line_buffer)*sizeof(char)+1); 
	//printf("%s", line_buffer);
	
	strcpy(history[history_length++], line_buffer);
	history[history_length-1][strlen(line_buffer)-1] = '\0';
	history_index = history_length-1;

	tty_term_mode();

  return line_buffer;
}