$ LIBHOSTS_FILE=~/.libhosts/hosts LD_PRELOAD=./libhosts.o ./resolveip a.b.c.d
IP address of a.b.c.d is 8.8.8.8
$
$ LIBHOSTS_DEBUG=1 LIBHOSTS_FILE=~/.libhosts/hosts LD_PRELOAD=./libhosts.o ./resolveip a.b.c.d
[+] libhosts: libhosts.c:30 gethostbyname(): First call
[+] libhosts: libhosts.c:34 gethostbyname(): looking for a.b.c.d
[+] libhosts: libhosts.c:45 gethostbyname(): read from local host a.b.c.d -> 8.8.8.8
[+] libhosts: libhosts.c:49 gethostbyname(): matched
IP address of a.b.c.d is 8.8.8.8
$
$ LIBHOSTS_DEBUG=1 LIBHOSTS_FILE=~/.libhosts/hosts LD_PRELOAD=./libhosts.o ./resolveip a.b.c.d.e
[+] libhosts: libhosts.c:30 gethostbyname(): First call
[+] libhosts: libhosts.c:34 gethostbyname(): looking for a.b.c.d.e
[+] libhosts: libhosts.c:45 gethostbyname(): read from local host a.b.c.d -> 8.8.8.8
[+] libhosts: libhosts.c:65 gethostbyname(): Not found in local hosts file
./resolveip: Unable to find hostid for 'a.b.c.d.e': host not found
$