#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <limits.h>

int execvp(const char *file, char *const argv[])
{
	const char *p, *z, *path = getenv("PATH");
	size_t l, k;

	errno = ENOENT;
	if (!*file) return -1;

	if (strchr(file, '/'))
		return execv(file, argv);

	if (!path) path = "/usr/local/bin:/bin:/usr/bin";
	k = strnlen(file, NAME_MAX+1);
	if (k > NAME_MAX) {
		errno = ENAMETOOLONG;
		return -1;
	}
	l = strnlen(path, PATH_MAX-1)+1;

	for(p=path; ; p=z) {
		char b[l+k+1];
		z = strchr(p, ':');
		if (!z) z = p+strlen(p);
		if (z-p >= l) {
			if (!*z++) break;
			continue;
		}
		memcpy(b, p, z-p);
		b[z-p] = '/';
		memcpy(b+(z-p)+(z>p), file, k+1);
		execv(b, argv);
		if (errno != ENOENT) return -1;
		if (!*z++) break;
	}
	return -1;
}