<CTRL-D> can be displayed, printed, sent, or whatever by chr(4). However, this won't fix your script, since 1) echo isn't a Perl command, 2) if it were, it wouldn't print to smbclient, which I assume you're trying to do, and 3) you shouldn't need to send a <CTRL-D> if you do IPC the right way. You need something like

!#/usr/bin/perl -w
use strict;

my ($victim, $message) = ("joe", "bloop");

# open an output pipe to the external program
open SMB, "| smbclient -M $victim";

# print on the pipe's handle
print SMB $message;

# close the handle, which implicitly sends an EOF
close SMB;
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Hope that helps.