my $outdata_v1 = "";
my $outdata_v2 = "";

my $data_offset = tell DATA;
my $line_count = 1;

print "First Regexp solution\n";
print "-"x20, "\n";
while ( <DATA> )
{
 $outdata_v1 .= $_;
 print "outdata for read of line $line_count before:\n$outdata_v1\n";
 $outdata_v1 =~ s{<cfmail}{<!--- <cfmail}g;
 $outdata_v1 =~ s{</cfmail>}{</cfmail> --->}g;
 print "outdata for read of line $line_count after:\n$outdata_v1\n";
 $line_count++;
}

#-- reset it all, start again with the better regexp.
seek( DATA, $data_offset, 0);
$line_count = 1;

print "Second Regexp solution\n";
print "-"x20, "\n";
while ( <DATA> ){
 $outdata_v2 .= $_;
 print "outdata for read of line $line_count before:\n$outdata_v2\n";
 $outdata_v2 =~ s{(?<!<!--- )<cfmail}{<!--- <cfmail}g;
 $outdata_v2 =~ s{</cfmail>(?! --->)}{</cfmail> --->}g;
 print "outdata for read of line $line_count after:\n$outdata_v2\n";
 $line_count++;
}


__DATA__
<cfmail to="#to_address#">
</cfmail>
<cfmail to="#to_address_2#">