[TxMt] csh: Bad : modifier in $ (/). /bin/bash: line 4: : command not found

[Jamie Forrest]

I am having trouble running a fairly simple Ruby program (below).   
The error that I get in TextMate is:

csh: Bad : modifier in $ (/). /bin/bash: line 4: : command not found

Here's the program (from David A. Black's Ruby for Rails book):
puts "Reading Celsius temperature value from data file...";
num = File.read("temp.dat");
c = num.to_i;
f = (c * 9/5) + 32;
puts "Saving result to output file temp.out";
fh = File.new("temp.out", "w");
fh.puts f;
fh.close;

I'm sure there's an easy fix.  Thanks,
Jamie Forrest