Simple FSM to strip Juniper configuration comments

junos_strip_comments.c

/**
 *  Strip Juniper Comments
 *  Copyright (C) 2011 Matous J. Fialka, <http://mjf.cz/>
 *  Released under the terms of The MIT License
 */

#include <stdio.h>

enum {
	ASCII_NUL = '\000',
	ASCII_BELL = '\007',
	ASCII_BACKSPACE = '\010',
	ASCII_HTTAB = '\011',
	ASCII_LFNL = '\012',
	ASCII_LINE_TABULATION = '\013',
	ASCII_FORM_FEED = '\014',
	ASCII_CR = '\015',
	ASCII_ESCAPE = '\033',
	ASCII_QUOTATION_MARK = '\042',
	ASCII_NUMBER_SIGN = '\043',
	ASCII_ASTERISK = '\052',
	ASCII_SOLIDUS = '\057',
	ASCII_DIGITAL_ZERO = '\060',
	ASCII_REVERSED_SOLIDUS = '\134',
	ASCII_DELETE = '\177',
	ASCII_MINISCULE_A = '\141',
	ASCII_MINISCULE_B = '\142',
	ASCII_MINISCULE_D = '\144',
	ASCII_MINISCULE_E = '\145',
	ASCII_MINISCULE_F = '\146',
	ASCII_MINISCULE_N = '\156',
	ASCII_MINISCULE_R = '\162',
	ASCII_MINISCULE_T = '\164',
	ASCII_MINISCULE_V = '\166'
};

int
main(void)
{
	enum {
		STATE_TEXT = 0,
		STATE_TEXT_REVERSED_SOLIDUS,
		STATE_TEXT_SOLIDUS,
		STATE_COMMENT,
		STATE_MULTILINE_COMMENT,
		STATE_MULTILINE_COMMENT_ASTERISK,
		STATE_QUOTATION,
		STATE_QUOTATION_REVERSED_SOLIDUS,
		STATE_ABORT
	} state;
	int position;

	state = STATE_TEXT;
	while((position = fgetc(stdin)) != EOF) {
		switch (state) {
		case STATE_TEXT:
			switch (position) {
			case ASCII_QUOTATION_MARK:
				state = STATE_QUOTATION;
				break;
			case ASCII_REVERSED_SOLIDUS:
				state = STATE_TEXT_REVERSED_SOLIDUS;
				continue;
			case ASCII_SOLIDUS:
				state = STATE_TEXT_SOLIDUS;
				continue;
			case ASCII_NUMBER_SIGN:
				state = STATE_COMMENT;
				continue;
			default:
				break;
			}
			break;
		case STATE_TEXT_REVERSED_SOLIDUS:
			switch (position) {
			case ASCII_LFNL:
				state = STATE_TEXT;
				continue;
			}
			state = STATE_TEXT;
			break;
		case STATE_TEXT_SOLIDUS:
			switch (position) {
			case ASCII_ASTERISK:
				state = STATE_MULTILINE_COMMENT;
				continue;
			default:
				state = STATE_TEXT;
				fputc(ASCII_SOLIDUS, stdout);
				break;
			}
			break;
		case STATE_COMMENT:
			switch (position) {
			case ASCII_LFNL:
				state = STATE_TEXT;
				break;
			default:
				continue;
			}
			break;
		case STATE_MULTILINE_COMMENT:
			switch (position) {
			case ASCII_ASTERISK:
				state = STATE_MULTILINE_COMMENT_ASTERISK;
				continue;
			default:
				continue;
			}
			break;
		case STATE_MULTILINE_COMMENT_ASTERISK:
			switch (position) {
			case ASCII_SOLIDUS:
				state = STATE_TEXT;
				continue;
			default:
				state = STATE_MULTILINE_COMMENT;
				continue;
			}
			break;
		case STATE_QUOTATION:
			switch (position) {
			case ASCII_QUOTATION_MARK:
				state = STATE_TEXT;
				break;
			case ASCII_REVERSED_SOLIDUS:
				state = STATE_QUOTATION_REVERSED_SOLIDUS;
				continue;
			default:
				break;
			}
			break;
		case STATE_QUOTATION_REVERSED_SOLIDUS:
			state = STATE_QUOTATION;
			switch (position) {
			case ASCII_DIGITAL_ZERO:
				putc(ASCII_NUL, stdout);
				continue;
			case ASCII_MINISCULE_A:
				putc(ASCII_BELL, stdout);
				continue;
			case ASCII_MINISCULE_B:
				putc(ASCII_BACKSPACE, stdout);
				continue;
			case ASCII_MINISCULE_D:
				putc(ASCII_DELETE, stdout);
				continue;
			case ASCII_MINISCULE_E:
				putc(ASCII_ESCAPE, stdout);
				continue;
			case ASCII_MINISCULE_F:
				putc(ASCII_FORM_FEED, stdout);
				continue;
			case ASCII_MINISCULE_N:
				putc(ASCII_CR, stdout);
				continue;
			case ASCII_MINISCULE_R:
				putc(ASCII_LFNL, stdout);
				continue;
			case ASCII_MINISCULE_T:
				putc(ASCII_HTTAB, stdout);
				continue;
			case ASCII_MINISCULE_V:
				putc(ASCII_LINE_TABULATION, stdout);
				continue;
			default:
				break;
			}
			break;
		case STATE_ABORT:
			break;
		default:
			break;
		}
		fprintf(stdout, "%c", position);
	}
	switch (state) {
	case STATE_TEXT_REVERSED_SOLIDUS:
		fprintf(stderr, "Error: end of file can not be escaped\n");
		return 1;
	case STATE_QUOTATION:
	case STATE_QUOTATION_REVERSED_SOLIDUS:
		fprintf(stderr, "Error: string not closed\n");
		return 1;
	case STATE_COMMENT:
		fprintf(stderr, "Error: comment not closed\n");
		return 1;
	case STATE_MULTILINE_COMMENT:
		fprintf(stderr, "Error: multiline comment not closed\n");
		return 1;
	default:
		return 0;
	}
}

Compile as follows:

cc -pedantic -ansi -Wall -Werror -o junos_strip_comments junos_strip_comments.c