Behead: remove email headers, and print the body to stdout.

behead.c

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

void behead(FILE *f);
void *end_of_line(char *line, size_t size, FILE *f);
void append(char *tmp, size_t size, const char *line, size_t len);

int main(int argc, char *argv[])
{
	FILE *f = stdin;
	bool f_is_stdin = true;

	if (argc > 1) {
		f = fopen(argv[1], "rb");
		f_is_stdin = false;
	}

	if (!f) {
		perror(argv[1]);
		exit(EXIT_FAILURE);
	}

	behead(f);

	if (!f_is_stdin) {
		fclose(f);
	}
	exit(EXIT_SUCCESS);
}

void append(char *tmp, size_t size, const char *line, size_t len)
{
	size_t i, j;

	--size;

	for (i = len; i < size; ++i) {
		tmp[i - len] = tmp[i];
	}

	for (i = size - len, j = 0; i < size && j <= len; ++i, ++j) {
		tmp[i] = line[j];
	}

	return;
}

void *end_of_line(char *line, size_t size, FILE *f)
{
	char *tmp = malloc(size);
	void *r;
	size_t len;

	if (!tmp)
		return NULL;

	r = (void *) fgets(line, size, f);

	if (line[0] == '\n' || !r)
		goto exit;

	len = strlen(line);
	while (len == 0 || line[len - 1] != '\n') {
		strncpy(tmp, line, size);
		if ((r = (void *) fgets(line, size, f)) == NULL)
			goto exit;
		len = strlen(line);
		append(tmp, size, line, len);
	}

	strncpy(line, tmp, size);

exit:
	if (tmp)
		free(tmp);
	return r;
}

void behead(FILE *f)
{
	char line[16];
	size_t chars_read;

	while (end_of_line(line, sizeof(line), f) != NULL)
		if (line[0] == '\n' && line[1] == '\0')
			break;

	while ((chars_read = fread(line, 1, sizeof(line), f)) > 0u) {
		size_t written = fwrite(line, 1, chars_read, stdout);
		if (written != chars_read)
			perror("written != read");
	}
}

Doesn't work with files with CRLF line endings for some reason.

Fixed. Oddly, I fixed this issue by not worrying about it, and ignoring it altogether.