Regarding the SQL query in duplicate_email(), unless there's a compelling need to return anything more than true or false, I'd change it to SELECT COUNT(*) FROM email WHERE email='$email'. Why make the database do more work than it needs, especially if you're returning the parameter you passed in if there are duplicates. :) (Hey, this isn't a big inefficiency unless you have an oustandingly large number of rows to return, but it's a good principle.)

Regarding Masem's suggestion for a dispatch table, instead of changing the function signatures for all of your subroutines, you can use anonymous subs:

my %functions = (
    default => sub { write_default($script_loc) }, 
    warning => sub { write_warning($script_loc, $email, $name, $warnin
+g_msg) },
    confirm => sub { write_confirm($script_loc, $email, $name) },
    commit  => sub { write_commit($email, $name) },
);
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Ahh, closures.

Update: mischief caught a missing curly brace.