Ruby solution for week 2, part 2

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diff --git a/challenge-002/abigail/ruby/ch-2.rb b/challenge-002/abigail/ruby/ch-2.rb
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+#!/usr/bin/ruby
+
+#
+# See ../README.md
+#
+ 
+#
+# Run as: ruby ch-2.rb {-f | -t} < input-file
+#
+
+require 'optparse'
+
+BASE = 35
+
+#
+# Parse and validate options
+#
+params = ARGV . getopts ('ft')
+do_from_base = params ["f"] ? 1 : 0
+do_to_base   = params ["t"] ? 1 : 0
+if do_from_base + do_to_base != 1
+    STDERR . puts "Program requires exactly one of '-f' or '-t'"
+    exit 1
+end
+
+
+def to_base (number)
+    out = ""
+    while number > 0 do
+        rest = number % BASE
+        if rest < 10
+        then char = rest . to_s
+        else char = (65 + rest - 10) . chr
+        end
+        out = char + out
+        number = (number / BASE) . to_i
+    end
+    return out
+end
+
+def from_base (number)
+    return number . to_i (35)
+end
+
+ARGF . each_line do |_|
+    if   do_from_base == 1
+    then puts from_base (_)
+    else puts to_base (_ . to_i)
+    end
+end