How to debug ruby code?

Question

I run Ubuntu 10.10. I just want to debug a simple script. After spending half a day trying to figure out how that could be done I give up. What the heck am I supposed to do?

Answer 1

Try default Ruby Debugger either by:

ruby -r debug filename[, ...] 

Or if it's CLI script, just change its first line from:

#!/usr/bin/env ruby

to:

#!/usr/bin/env ruby -rdebug

and the script will stop on each Exception.

Or check the following script sample:

#!/usr/bin/env ruby
class Hello
   def initialize( hello )
      @hello = hello
   end
   def hello
      @hello
   end
end

salute = Hello.new( "Hello, Mac!" )
puts salute.hello

You can debug it as shown below:

# ruby -r debug hello.rb
Debug.rb
Emacs support available.

hello.rb:3:class Hello
(rdb:1) v l
  salute => nil
(rdb:1) b 10
Set breakpoint 1 at hello.rb:10
(rdb:1) c
Hello, Mac!

Source: Ruby Debugger

---

Alternatively use lldb/gdb. See below the simple example to print script backtrace into foreground:

echo 'call (void)rb_backtrace()' | lldb -p $(pgrep -nf ruby)

^{Replace lldb with gdb if works better. Prefix with sudo to debug non-owned process.}