The keys of the hash are defined:

lorien:~$ perl -le 'print %!'
EBADR0ENOMSG0ENOTSUP0ESTRPIPE0EADDRINUSE0EL3HLT0EBADF0ENAVAIL0ECHRNG0E
+NOTBLK0ENOTNAM0ELNRNG0EXDEV0EBADE0EBADSLT0ECONNREFUSED0ENOSTR0EISCONN
+0EOVERFLOW0ENONET0EFBIG0ECONNRESET0ELIBMAX0EWOULDBLOCK0EREMOTEIO0ENOP
+KG0ELIBSCN0EMEDIUMTYPE0EDESTADDRREQ0ENOTSOCK0EIO0EINPROGRESS0ERANGE0E
+ADDRNOTAVAIL0EAFNOSUPPORT0EINTR0EILSEQ0EREMOTE0ENOMEM0ENETUNREACH0EPI
+PE0ENODATA0EUSERS0EOPNOTSUPP0EPROTO0EISNAM0ESPIPE0EALREADY0ENAMETOOLO
+NG0ENOEXEC0EISDIR0EBADRQC0EEXIST0EDOTDOT0ELIBBAD0ESRCH0EFAULT0EAGAIN0
+EDEADLOCK0EXFULL0ENOPROTOOPT0ENETDOWN0EPROTOTYPE0EL2NSYNC0ENETRESET0E
+ADV0EUCLEAN0EROFS0ESHUTDOWN0EMULTIHOP0EPROTONOSUPPORT0ENFILE0ENOLCK0E
+CONNABORTED0ECANCELED0EDEADLK0ENOLINK0ESRMNT0ENOTDIR0ETIME0EINVAL0ENO
+TTY0ENOANO0ELOOP0ENOENT0EPFNOSUPPORT0EBADMSG0ENOMEDIUM0EL2HLT0EDOM0EB
+FONT0EMSGSIZE0ENOCSI0EL3RST0ENOSPC0EIDRM0ENOBUFS0ENOSYS0EHOSTDOWN0EBA
+DFD0ENOSR0ENOTCONN0ESTALE0EDQUOT0EMFILE0EACCES0EBUSY0EPERM0E2BIG0ELIB
+EXEC0ETOOMANYREFS0ELIBACC0ENOTUNIQ0ECOMM0ERESTART0EUNATCH0ESOCKTNOSUP
+PORT0ETIMEDOUT0ENXIO0ETXTBSY0ENODEV0EMLINK0ECHILD0EHOSTUNREACH0EREMCH
+G0ENOTEMPTY0
[download]

Update:

lorien:~$ perl -v
This is perl, v5.8.0 built for i386-linux-thread-multi
[download]

Well its just for fun when i read in perlvar about %! and the last news about sendmail and bind it just comes to my head, ode to sendmail and bind here it is.
$anarion=\$anarion;

s==q^QBY_^=,$_^=$[x7,print

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