repl.c

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

typedef struct {
	char *buffer;
	size_t buffer_length;
	ssize_t input_length;
} InputBuffer;

InputBuffer *new_input_buffer() {
	InputBuffer *input_buffer = (InputBuffer *)malloc(sizeof(InputBuffer));
	input_buffer->buffer = NULL;
	input_buffer->buffer_length = 0;
	input_buffer->input_length = 0;
	
	return input_buffer;
}

void print_prompt() { printf("db >"); }

void read_input(InputBuffer *input_buffer) {
	ssize_t bytes_read = 
		getline(&(input_buffer->buffer), &(input_buffer->buffer_length), stdin);
	if (bytes_read <= 0) {
		printf("Error reading input\n");
		exit(EXIT_FAILURE);
	}

	// Ignore trailing newline
	input_buffer->input_length = bytes_read - 1;
	input_buffer->buffer[bytes_read - 1] = 0;
}

void close_input_buffer(InputBuffer *input_buffer) {
	free(input_buffer->buffer);
	free(input_buffer);
}

int main(int argc, char *argv[]) {
	InputBuffer *input_buffer = new_input_buffer();
	while (true) {
		print_prompt();
		read_input(input_buffer);

		if (strcmp(input_buffer->buffer, ".exit") == 0) {
			close_input_buffer(input_buffer);
			exit(EXIT_SUCCESS);
		} else {
			printf("Unrecognized command '%s'.\n", input_buffer->buffer);
		}
	}
}