C program that removes escaped line breaks, which are surrounded by double quotes from CSV file and change it into unix style file format (using line feed (LF) as line break). This program implements an automaton that accepts CSV, so it's short and run fast.

CSV_linebreak_fix.c

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

/* Size of atomic reads. */
#define BUFFER_SIZE (16 * 1024)

int state = 0;

void exit_with_error(int state, char c) {

  fprintf(stderr, "error when %d (%x)", state, c);
	exit(-1);
}

/*

Qs={0}, Qf={7}

0: (init)
1: "
2: (any character)
3: "
4: "
5: ,
6: EOF
7: CR
8: LF

0	1
1	2 3
2	2 3
3	4 5 6 7 8
4	2 3
5	1
7	1 6 8
8	1 6

*/

int main() {

	char buf[BUFFER_SIZE + 1];
	size_t bytes_read;

	while (0 < (bytes_read = read(0, buf, BUFFER_SIZE))) {

		int i;
		for (i = 0; i < bytes_read; i ++) {

			char next = buf[i];
			switch(state) {
				case 0:
					if (next == '"') {
						state = 1;
						putchar(next);
					}
					else {
						exit_with_error(state, next);
					}
					break;
				case 1:
					/* Fall through */
				case 2:
					/* Fall through */
				case 4:
					if (next == '"') {
						state = 3;
						putchar(next);
					}
					else {
						state = 2;

						// CR/LFは空白を出力
						if (next == 0x0D || next == 0x0A) {
							putchar(' ');
						}
						else {
							putchar(next);
						}
					}
					break;
				case 3:
					if (next == '"') {
						state = 4;
						putchar(next);
					}
					else if (next == ',') {
						state = 5;
						putchar(next);
					}
					else if (next == EOF) {
						state = 6;
						exit(0);
					}
					else if (next == 0x0D) {
						// CRを出力しない
						state = 7;
						//putchar(next);
					}
					else if (next == 0x0A) {
						state = 8;
						putchar(next);
					}
					break;
				case 5:
					if (next == '"') {
						state = 1;
						putchar(next);
					}
					else {
						exit_with_error(state, next);
					}
					break;
				case 7:
					if (next == EOF) {
						state = 6;
						exit(0);
					}
					else if (next == '"') {
						state = 1;
						putchar(next);
					}
					else if (next == 0x0A) {
						state = 8;
						putchar(next);
					}
					else {
						exit_with_error(state, next);
					}
					break;
				case 8:
					if (next == EOF) {
						state = 6;
						exit(0);
					}
					else if (next == '"') {
						state = 1;
						putchar(next);
					}
					else {
						exit_with_error(state, next);
					}
					break;
				default:
					exit_with_error(state, next);
					break;
			}
		}
	}

	//printf("finish!\n");
	exit(0);
}