FENIX_coreutils/echo.c

#define _POSIX_C_SOURCE 200809L

#include <stdio.h>

int ctoi(char c); /* A bit of a helper function */

int main(int argc, char ** argv) {
  int i, j, oct_temp;
  char char_temp;
	/*
		If /c is present in the text, we're not supposed to print a trailing
		newline at the end. Otherwise, we do. Hence, we start with 1 (true)
		for printing this and switch it to 0 if \c shows up
	*/
  int trailing_newline = 1;

	/* 
		Outer loop handles each word passed in, 
		inner loop handles characters within each word. 
	*/
  for(i = 1; i < argc; i++) {
    for(j = 0; argv[i][j] != '\0'; j++) {
			/* We need to handle escape sequences ourself. */
      if(argv[i][j] == '\\') {
				j++;
				switch(argv[i][j]) {
					case 'a': printf("\a"); break; /* alert */
					case 'b': printf("\b"); break; /* backspace */
					case 'c': trailing_newline = 0; break; /* suppress trailing newline */
					case 'f': printf("\f"); break; /* form feed */
					case 'n': printf("\n"); break; /* new line */
					case 'r': printf("\r"); break; /* carriage return */
					case 't': printf("\t"); break; /* horizontal tab */
					case 'v': printf("\v"); break; /* vertical tab */
					case '\\': printf("\\"); break; /* just print a backslash */
					/* Octal sequences */
					case '0': {
						j++;
						oct_temp = ctoi(argv[i][j]); /* 1 digit escape (e.g. 08) */
						j++;
						/* 2 digit escape (e.g. 063) */
						if(ctoi(argv[i][j] != -1)) {
							oct_temp *= 8;
							oct_temp += ctoi(argv[i][j]);
							j++;
							/* 
								3 digit escape (e.g. 0127)
								This is all the POSIX spec allows.
							*/
							if(ctoi(argv[i][j] != -1)) {
								oct_temp *= 8;
								oct_temp += ctoi(argv[i][j]);
							} 
							else {
								j--;
							}
						} 
						else {
							j--;
						}
						printf("%c", (char)oct_temp);
					}
					break;
				/* On unrecognized escape, just print it literal */
				default: printf("\\%c", argv[i][j]);
					break;
				}
      }
      else {
				printf("%c", argv[i][j]); /* Not a backslash? Print the character */
      }
    }
  }

	/* Print trailing newline */
  if(trailing_newline) {
    printf("\n");
  }

  return 0;
}

/* 
	I'm really not sure whether writing a ctoi function was ideal here.
	Maybe I should have just used atoi? I dunno. But, at this point, I'm
	just gonna leave it as is.

	- Kat
*/
int ctoi(char c) {
  switch(c) {
    case '0': return 0;
    case '1': return 1;
    case '2': return 2;
    case '3': return 3;
    case '4': return 4;
    case '5': return 5;
    case '6': return 6;
    case '7': return 7;
    case '8': return 8;
    case '9': return 9;
    default: return -1;
  }
}