2 files changed, 32 insertions, 1 deletions
diff --git a/Makefile b/Makefile
index afa20d6..b207c9f 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 BINDIR = $(HOME)/bin
 
-TARGETS = mkheader.py
+TARGETS = mkheader.py isprime
 
 all: $(TARGETS)
 	@echo "Nothing to be done"
diff --git a/isprime b/isprime
new file mode 100755
index 0000000..1f34dcc
--- /dev/null
+++ b/isprime
@@ -0,0 +1,31 @@
+#!/usr/bin/ruby
+
+def is_prime(n)
+	if n <= 2
+		return true
+	elsif n.modulo(2) == 0
+		return false
+	else
+		3.step(Math.sqrt(n).ceil, 2) do |i|
+			if n.modulo(i) == 0
+				return false
+			end
+		end
+		return true
+	end
+end
+
+if ARGV.length < 1
+	puts "Usage: isprime number [number...]"
+else
+	ARGV.each do |n|
+		if n.to_i < 1
+			puts "Negative numbers and 0 not allowed."
+			exit
+		elsif is_prime(n.to_i)
+			puts n.to_s + " is prime"
+		else
+			puts n.to_s + " is not prime"
+		end
+	end
+end