Catching line numbers in ruby exceptions

Consider the following ruby code

test.rb:

begin

  puts
  thisFunctionDoesNotExist
  x = 1+1
rescue Exception => e
  p e
end

For debugging purposes, I would like the rescue block to know that the error occurred in line 4 of this file. Is there a clean way of doing that?

p e.backtrace 

I ran it on an IRB session which has no source and it still gave relevant info.

=> ["(irb):11:in `foo'", 
    "(irb):17:in `irb_binding'", 
     "/usr/lib64/ruby/1.8/irb/workspace.rb:52:in `irb_binding'", 
     "/usr/lib64/ruby/1.8/irb/workspace.rb:52"]

If you want a nicely parsed backtrace, the following regex might be handy:

p x.backtrace.map{ |x|   
     x.match(/^(.+?):(\d+)(|:in `(.+)')$/); 
    [$1,$2,$4] 
}

[  ["(irb)", "11", "foo"], 
  ["(irb)", "48", "irb_binding"], 
  ["/usr/lib64/ruby/1.8/irb/workspace.rb", "52", "irb_binding"], 
  ["/usr/lib64/ruby/1.8/irb/workspace.rb", "52", nil]
]

( Regex /should/ be safe against weird characters in function names or directories/filenames ) ( If you're wondering where foo camefrom, i made a def to grab the exception out :

>>def foo
>>  thisFunctionDoesNotExist
>> rescue Exception => e 
>>   return e 
>>end     
>>x = foo 
>>x.backtrace

You can access the backtrace from an Exception object. To see the entire backtrace:

p e.backtrace

It will contain an array of files and line numbers for the call stack. For a simple script like the one in your question, it would just contain one line.

["/Users/dan/Desktop/x.rb:4"]

If you want the line number, you can examine the first line of the backtrace, and extract the value after the colon.

p e.backtrace[0].split(":").last

Usually the backtrace contains a lot of lines from external gems It's much more convenient to see only lines related to the project itself

My suggestion is to filter the backtrace by the project folder name

puts e.backtrace.select { |x| x.match(/HERE-IS-YOUR-PROJECT-FOLDER-NAME/) }

And then you can parse filtered lines to extract line numbers as suggested in other answers.

Throwing my $0.02 in on this old thread-- here's a simple solution that maintains all the original data:

print e.backtrace.join("\n")

It is possible that in Ruby 1.9.3 you will be able to get access to not only this information in a more structured, reliable, and simpler way without using regular expressions to cut strings.

The basic idea is to introduce a call frame object which gives access to information about the call stack.

See http://wiki.github.com/rocky/rb-threadframe/, which alas, requires patching Ruby 1.9. In RubyKaigi 2010 (late August 2010) a meeting is scheduled to discuss introducing a frame object into Ruby.

Given this, the earliest this could happen is in Ruby 1.9.3.