strace perl -e 'gethostbyname "bahn.de"'  2>&1 | grep open | grep -v NOENT
...
open("/etc/resolv.conf", O_RDONLY)      = 3
open("/etc/nsswitch.conf", O_RDONLY)    = 3
open("/etc/ld.so.cache", O_RDONLY)      = 3
open("/lib64/libnss_files.so.2", O_RDONLY) = 3
open("/etc/host.conf", O_RDONLY)        = 3
open("/etc/hosts", O_RDONLY|O_CLOEXEC)  = 3
open("/etc/ld.so.cache", O_RDONLY)      = 3
open("/lib64/libnss_dns.so.2", O_RDONLY) = 3
open("/lib64/libresolv.so.2", O_RDONLY) = 3