Sams Teach Yourself Ruby in 21 Days

Stack Traces

When a script fails with an exception message, that message provides a description of the problem, in terms that may or may not make immediate sense to you. An exception message appears along with something called a stack trace, which is a kind of history of method calls going back to the top-level script.

The script in Listing C.1 has a problem (besides being obfuscated, contrived, and otherwise useless, that is) that prevents it from running to completion.

Listing C.1. div0.rb

#!/usr/bin/env ruby def foo return 4.0/baz(20) end def baz(n) sum = 0 n.times do |i| sum += quux(i) end return n + sum end def quux(v) return 9/(5-v) end puts foo

The Ruby interpreter produces the following information when trying to run the script: