+sub __eval_option {
+ my ($option, $i) = @_;
+
+ # Add space to evaluate the character before $
+ $option = " $option";
+ my $retval = "";
+
+ while ($option =~ /(.*?[^\\])\$\{(.*?)\}(.*)/) {
+ my $start = $1;
+ my $var = $2;
+ my $end = $3;
+
+ # Append beginning of line
+ $retval = "$retval$start";
+
+ # If the iteration option OPT[$i] exists, then use that.
+ # otherwise see if the default OPT (without [$i]) exists.
+
+ my $o = "$var\[$i\]";
+
+ if (defined($opt{$o})) {
+ $o = $opt{$o};
+ $retval = "$retval$o";
+ } elsif (defined($opt{$var})) {
+ $o = $opt{$var};
+ $retval = "$retval$o";
+ } else {
+ $retval = "$retval\$\{$var\}";
+ }
+
+ $option = $end;
+ }
+
+ $retval = "$retval$option";
+
+ $retval =~ s/^ //;
+
+ return $retval;
+}
+
+sub eval_option {
+ my ($option, $i) = @_;
+
+ my $prev = "";
+
+ # Since an option can evaluate to another option,
+ # keep iterating until we do not evaluate any more
+ # options.
+ my $r = 0;
+ while ($prev ne $option) {
+ # Check for recursive evaluations.
+ # 100 deep should be more than enough.
+ if ($r++ > 100) {
+ die "Over 100 evaluations accurred with $option\n" .
+ "Check for recursive variables\n";
+ }
+ $prev = $option;
+ $option = __eval_option($option, $i);
+ }
+
+ return $option;
+}
+