Question

I want to watch the flow the execution of my ruby code when I am in the console. For example, if I have this :

def process
  hash = {a:1,b:2}
  hash.values.map!{|e| e+1}
end

And I want to see something like this in console when I type process :

hash = {a:1,b:2}
=> {:a=>1, :b=>2}
hash.values.map!{|e| e+1}
=> [2, 3]

Is there a useful way to do something like this?

$VERBOSE doesn’t seems to do anything and $DEBUG seems as the opposite to be too verbose.

Answer 1

You’re talking about “trace” functionality.

Some languages, like shell and good-ol’ GWBasic, have a flag to show their currently executing line. Ruby’s $DEBUG output can flood you with information overload, not so much from your code, but from any gems that look for it and dump their current state or turn on their tracing.

Many people sprinkle their code with puts to have it show some indicator of where they are, during their development/testing. If you do that, I’d recommend writing it as a method to bottleneck your output and let you easily turn it on/off. Also, use a flag to check whether you want to debug. You might even want to use OptionParser to let you create a --debug flag to pass on the command-line. Another nice side-effect of using a method is it’s easy to redirect the output to a file you can tail and watch the output as it occurs, and later use for triage.

Another alternative is to load the code into the debugger and tell it to trace. You’ll see every step of the code, which is very verbose, but the detail is good. You can also tell it to run to certain points so you can poke at the code and dig around, dropping into IRB if needed.

Personally, being old-school and having cut my teeth on assembly-language, I’m comfortable in debuggers, so I use Ruby’s a lot. It’s easy to tell it to run to a certain spot and stop, or you can embed include 'debugger'; debugger into your code and it’ll stop at that point. Once there, it’s possible to see what’s going on, then c to continue, and let the program run until it hits the debugger statement again. I find the debugger to be very powerful and a nice selective magnifying glass for those times I want to know what’s going on.

“Debugging in Ruby” has lots of nice tips you might find useful too.

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EDIT:

I like Alex D’s suggestion to look into Ruby’s set_trace_func. I haven’t used it (and, frankly forgot about it), but that’d be a good way to set up a nice trace in an app. With a little code you could set up toggling it on/off and selectively outputting given a certain class or condition since you’re in control of the proc being called.