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

#define IS_SPECIAL(c) (c == ' ' ? 1 :   \
                       c == '&' ? 1 :   \
                       c == '<' ? 1 :   \
                       c == '|' ? 1 :   \
                       c == '"' ? 1 : 0)

static char *
escape_quoting(const char* arg)
{
    char dq_on, seen_bs;
    char *ptr, *ret, *ret_ptr;

    /* New(1310, ret, strlen(ptr) + 1, char); */
    ret     = (char*) malloc(strlen(ptr) + 1);
    ret_ptr = ret;

    for(dq_on = 0, seen_bs = 0, ptr = (char*)arg; *ptr != '\0'; ptr++) {
        if('\\' == *ptr && 0 == seen_bs) {
            seen_bs = 1;
            continue;
        }
        
        if('\\' == *ptr && 1 == seen_bs)
            seen_bs = 0;

        if('"' == *ptr && 0 == seen_bs && 0 == dq_on) {
            dq_on = 1;
            continue;
        }
        
        if(1 == dq_on && IS_SPECIAL(*ptr)) {
            if(*(ptr + 1) != '\0' && '"' == *(ptr + 1))
                *ret_ptr++ = *ptr++;
            dq_on = 0;
            continue;
        }
        
        *ret_ptr++ = *ptr;
        dq_on = seen_bs = 0;
    }
    
    *ret_ptr = '\0';

    return ret;
}

int main(void) {
    char arg1[] = "print\"\"\"foo\" \"bar\"\"\"";
    char arg2[] = "print\"\"\"\"foo bar\"\"\"\"";
    char arg3[] = "\"print\\\"foo bar\\\"";
    char arg4[] = "\"print\\\"foo bar\\\"\"";
    char arg5[] = "print\\\"foo\" \"bar\\\"";
    char arg6[] = "print'\"\"\"\"\"\"\"\"'";
    char arg7[] = "\"print \\\"\\\\\\\"\\\\\\\"\\\"";
    char *quoted;

    quoted = escape_quoting(arg1);
    printf("%s\n", quoted);
    free(quoted);

    quoted = escape_quoting(arg2);
    printf("%s\n", quoted);
    free(quoted);

    quoted = escape_quoting(arg3);
    printf("%s\n", quoted);
    free(quoted);

    quoted = escape_quoting(arg4);                                               
    printf("%s\n", quoted);
    free(quoted);

    quoted = escape_quoting(arg5);
    printf("%s\n", quoted);
    free(quoted);

    quoted = escape_quoting(arg6);
    printf("%s\n", quoted);
    free(quoted);

    quoted = escape_quoting(arg7);
    printf("%s\n", quoted);
    free(quoted);

    return 0;
}