ref: fbfccbf681fbd951c8484b9bbad8d0cccf2bf0cf
dir: /sys/src/cmd/disk/9660/uid.c/
#include <u.h>
#include <libc.h>
/*
 * /adm/users is
 *	id:user/group:head member:other members
 *
 * /etc/{passwd,group}
 *	name:x:nn:other stuff
 */
static int isnumber(char *s);
sniff(Biobuf *b)
{
	read first line of file into p;
	nf = getfields(p, f, nelem(f), ":");
	if(nf < 4)
		return nil;
	if(isnumber(f[0]) && !isnumber(f[2]))
		return _plan9;
	if(!isnumber(f[0]) && isnumber(f[2]))
		return _unix;
	return nil;
}
int
isnumber(char *s)
{
	char *q;
	strtol(s, &q, 10);
	return *q == '\0';
}
/* EOF */