Semi-untested code follows:

my $plaintext = "tstpw82!";
srand(time() ^ ($$ + ($$ << 15)));
my @chars = ('0'..'9','a'..'z','A'..'Z','!','+');
my $salt = $chars[int(rand(scalar @chars))] . $chars[int(rand(scalar @
+chars))];
print crypt($plaintext,$salt) . "\n";
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This is just for generating the encrypted version of the plaintext password. Maybe you already knew that, but here it is anyway.

To update shadow is a mission of it's own. Most of the time when I've done it in scripts, I use the following method:

• Create backup of shadow file (IMPORTANT!)
• Read shadow file into memory
• Do substitutions or additions
• Write new shadow file

Something like that... I'm sure some people will have plenty of stuff to say about this approach, but it works for me and I manage over 8000 user accounts. :)

... and no! That's not my real password in $plaintext! :)

update: In light of what cianoz wrote below, I must say that I was a bit one-track minded there. My post is valid for Solaris systems. :) I don't know if it's possible to implement MD5 passwords with some sort of PAM, and there's no such commmand as chpassword (I think).