The idea is to use perl syntax and the perl parser for the substitution, rather than a made up syntax (e.g. %NAME% and s/%NAME%/$name/). Is this crazy?

Yes, that's crazy, because:

• Neither string eval nor block eval will really work the way you think you want it to here.

• Even if eval did work this way (which it doesn't) this approach would require that you maintain a tricky and easy-to-break dependency between the template text and the perl script: the author of the text needs to know the names and the nature of specific variables (and hash keys) in the perl script, and typos will create unpredictable results that you really don't want in a form letter.

• As others have mentioned, taking a string from a file (or from a database) and passing it to eval poses some risk: it's not just that things might go horribly wrong, it's also an issue that getting things to come out right may be ridiculously hard. (update: note that eval will treat "-" as the subtraction operator, "." as the concatenation operator, etc, so simple punctuation becomes a hazard)

You'll be better off with an approach that generalizes more easily. In what you have so far, the form letter text and the per-recipient data fields come from external sources (a file and a database, respectively) rather than being hard-coded in the script, and that's good.

The next step is to work out a way to externalize the relation between the form and the field data, so that this doesn't depend on how the perl script is written. If the template uses some easily recognized pattern for the field data (like "Dear %NAME%", etc), the perl script can pull these out automatically without needing to worry about how they are spelled; if these names happen to match the column names in the database, things get even easier for the script:

{    # limit the scope of $/ being undef
  local $/;  
  $block = <FILE>
}

my %template_flds = ( EMAIL => undef ); # just in case %EMAIL% is not 
+in the template

while ( $block =~ /\%(\w+)\%/g ) {
    $template_flds{$1} = undef;
}
my @query_flds = sort keys %template_flds;

$sql = "select ".join(',',@query_flds)." from database";
while( $row = getrow( $sql )) {
    my $mesg = $block;
    for ( @query_flds ) {
        $mesg =~ s/\%$_\%/$row->{$_}/g;
    }
    print "Sending to $row->{EMAIL}\n";
    send_email( $row->{EMAIL}, $mesg );
}
[download]

Here, only three dependencies are hard-coded: the name of the database table that holds the field data, the general form of the query string (simple select of columns from a single table with no joins or "where" conditions), and the fact that the database table needs to have a column called EMAIL.

When I wrote my own form-letter app like this, I chose to externalize the query as well. My script used two inputs: the template file, and a tab-delimited flat file (the recipient list) whose first column -- potentially the only column -- was always the email address. If there were more columns in the list, the first row/line in the list had to be a header that assigned a name to each column, and each distinct "%\w+%" string in the template had to exist in the header row, or the script would die with an error message.

Doing it that way means that the query for form data can be arbitrarily complex, so long as it delivers a simple tab-delimited report with one recipient per row; and it's entirely up to the user (not the programmer) to make sure that the template content and per-recipient data are compatible with one another.

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