Not to be a heretic, but you could step outside of Perl and just use the "shar" program to create a shell archive. This utility already does near-exactly what you're trying to do, and is (somewhat) common.

Here's the HP/UX "shar:"

 usage: shar [-AabCcDdefhmorstuvZ] <file|dir> ...
 -A:             supress warning messages for optional acl entries
 -a:             assume files are shippable, don't uuencode
 -b:             use basenames instead of full pathnames
 -c:             use wc(1) to check integrity of transfer
 -C:             include a "cut here" line
 -d:             don't recurse on contents of directories
 -D <dir>:       must be in <dir> to unpack
 -e:             don't overwrite existing files
 -f <file>:      file containing list of directories and  files
                 or - to read filenames from standard input
 -h              follow symbolic links instead of archiving  them
 -m:             retain modification/access times on files
 -o:             retain user/group owner information
 -r:             must be "root" to unpack
 -s:             use sum(1) to check integrity of transfer
 -t:             verbose messages to /dev/tty instead of  stderr
 -u:             assume remote site has uudecode(1) for  unpacking
 -v:             verbose mode
 -Z:             shrink files using compress(1)
[download]

The GNU version is substantially similar.

If your "targets" don't have access to a POSIX-like shell, though, they'd need one. (i.e. are they stuck on Windows?) The Bourne Again Shell (bash) from Cygwin comes to mind...

For example:

(hpux) $ shar myfile.pl > myfile.shar

(nt) $ ftp (hpux)
Connected to (hpux)
220 (hpux) FTP server (Version 1.1.214.4 Mon Feb 15 08:48:46 GMT 1999)
+ ready.
Name ((hpux):(user)):
331 Password required for (user).
Password:
230 User (user) logged in.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ascii
200 Type set to A.
ftp> get sample.shar
200 PORT command successful.
150 Opening ASCII mode data connection for sample.shar (138630 bytes).
226 Transfer complete.
140877 bytes received in 0.14 seconds (1006264 bytes/s)
ftp> quit
221 Goodbye.

administrator@(nt) ~
$ head -3 sample.shar

# This is a shell archive.  Remove anything before this line,
# then unpack it by saving it in a file and typing "sh file".

administrator@(nt) ~
$ sh sample.shar
Compiling unpacker for non-ascii files
x - myfile.pl
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I've assumed a binary file here (ergo the line about non-ascii), but transfered it in ASCII mode, just to make sure that the translation before a 64-bit UNIX host and a 32-bit Win32 host would work OK even over an "unclean" link, like contained in an eMail message. Something like this should work for you, then:

#!/usr/bin/perl -w
my $recipients = 'admin@site1 admin@site2';
open MAIL, "|mailx -s 'updated files' $recipients";
print MAIL<<HEADER_END;

Here are today's updated files.

Save the rest of this message to a file (for example, "updated.shar") 
+and then run it in a shell (for example,
"sh updated.shar") to extract.

HEADER_END
print MAIL `shar @ARGV`;
print MAIL `cat ~/.signature`;
close MAIL;
[download]