Question

I’m writing a Ruby C extension, and frequently need to run GDB or Valgrind to find bugs. For debugging my specs, I use this:

namespace :spec do  
  RSPEC_CMD = [ 'ruby', '-S', 'rspec', '-Ilib:ext', SPECDIR ]

  desc "Run specs under GDB."
  task :gdb => [ :compile ] do |task|
          cmd = [ 'gdb' ] + GDB_OPTIONS
          cmd += [ '--args' ]
          cmd += RSPEC_CMD
          run( *cmd )
  end

  desc "Run specs under Valgrind."
  task :valgrind => [ :compile ] do |task|
          cmd = [ 'valgrind' ] + VALGRIND_OPTIONS
          cmd += RSPEC_CMD
          run( *cmd )
  end
end

Unfortunately, that won’t work for IRB, since IRB is a Ruby script and not an executable.

I imagine the answer is extremely trivial, but I don’t know enough shell magic to figure it out on my own.

A caveat is that I need to be able to use IRB (enter commands), not just run IRB.

So what’s the command to run IRB within GDB (or Valgrind)?

Answer 1

Looking at the /usr/bin/irb I have here (using which irb), it just has the shebang #!/usr/bin/ruby1.8 in the first line (ie. in this case, /usr/bin/ruby1.8 is the actual executable file run). So you would give that to gdb:

$ gdb -- /usr/bin/ruby1.8

And then you could specify /usr/bin/irb as an argument for Ruby, giving you the irb prompt, thus:

(gdb) run /usr/bin/irb
Starting program: /usr/bin/ruby1.8 /usr/bin/irb
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
irb(main):001:0> print "Hello world\n"
Hello world
=> nil
irb(main):002:0> 

Also, I find this one-liner works for me:

$ gdb -ex run --args /usr/bin/ruby1.8 /usr/bin/irb