I would use Expect.pm to communicate with your system's passwd program, which always knows which kind of hash to use, and which may be PAM-enabled to update the password in more places that just /etc/shadow.

Working example code, loosely tested (needs more error checking). 

#!/usr/bin/perl -w
use strict;
use Expect;
my @user_pass_pairs = (
  [ qw( Tarzan Ungowa    ) ],
  [ qw( Jane   GoneNative) ],
);
# Time out if we don't get responses within 5 seconds.
my $timeout = 5;
foreach (@user_pass_pairs) {
  my ($user, $pass) = @$_;
  system('useradd', $username) == 0 or die;
  my $xp = Expect->spawn("passwd $user") or die;

  $xp->expect($timeout,"New UNIX password: ") or die;
  print $xp "$pass\r";
  
  $xp->expect($timeout,"Retype new UNIX password: ") or die;
  print $xp "$pass\r";

  $xp->expect(
    $timeout,"passwd: all authentication tokens updated successfully."
  ) or die;

}

[download]

In previous questions, some notable other suggestions were:

Those previous questions were:

In reply to Re: Shadow Passwords by Util
in thread Shadow Passwords by Anonymous Monk

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