added post-processing script to allow for conditional inclusion of gcode

utils/slic3r-conditional.pl

@@ -0,0 +1,23 @@
+#!/usr/bin/perl -i
+# Conditional gcode post-processor
+# Written by Joseph Lenox
+# Executes statements beginning with ;_if
+# the condition must be evaluatable Perl. 
+# If it's true, then print contents of the line after the second ; until end of line.
+# Else print nothing.
+use strict;
+use warnings;
+# regex: ^;_if (.* = .*);
+while (<>) {
+  if ($_ =~ m/^;[ ]*_if/) {
+    my @tokens = split(/;/, $_);
+    # modify $_ here before printing
+    my $condition = $tokens[1] =~ s/_if//r;
+    if (eval($condition)) {
+      $_ = join('', @tokens[2..$#tokens]);
+    } else {
+      $_ = "";
+    }
+  }
+  print;
+}