diff --git a/prime.pl b/prime.pl
new file mode 100755
index 0000000..0c5f727
--- /dev/null
+++ b/prime.pl
@@ -0,0 +1,40 @@
+#!/usr/bin/env perl
+
+#   prime number calculation
+# author: david@socialnerds.org
+
+my $num = 3;
+print "highest prime number: ";
+chomp(my $maxnum = <STDIN>);
+my $count = 2;
+
+print "2\n3\n";
+
+while ( $num <= $maxnum )
+{
+    $i=3;
+    while ( $i <= int($num**(1/2)+1) )
+    {
+        if ( $i != 1 && $i < $num && $i%2 != 0 )
+        {
+            if ( $num % $i != 0 ) {
+                $probably = "true"
+            } else {
+                $probably = "false";
+                last;
+            }
+        }
+        $i += 2;
+    }
+
+    if ( $probably eq "true" )
+    {
+        print "$num\n";
+        $count++;
+    }
+    $num += 2;
+}
+
+print "prime number count: $count\n";
+
+
diff --git a/reference.pl b/reference.pl
new file mode 100755
index 0000000..20baab3
--- /dev/null
+++ b/reference.pl
@@ -0,0 +1,52 @@
+#!/usr/bin/env perl
+
+use 5.010;
+
+my $var = 5*5;
+
+chomp(my $input = <STDIN>);
+
+$var *= $input;
+
+if ( $var == 100 )
+{
+    say $var;
+}
+else
+{
+    say "it is not 100";
+}
+
+$is_true = $var == 100;
+
+if ( ! $is_true )
+{
+    say "not true";
+}
+else
+{
+    say "true";
+}
+
+my $zaehler=0;
+while ($zaehler <= 5)
+{
+    say "der zähler steht jetzt auf $zaehler";
+    $zaehler += 1;
+}
+
+chomp(my $input2 = <STDIN>);
+if ( defined($input2) )
+{
+    say "eingabe lautet: $input2";
+}
+else
+{
+    say "keine eingabe verfügbar";
+}
+
+#umfang berechnung
+print "bitte radius für umfangberechnung angeben: ";
+chomp(my $radius = <STDIN>);
+my $umfang = $radius *= 2*3.141592654;
+say "umfang beträgt: $umfang";