# Rescue clause

**URL:** <https://www.ruby-forum.com/t/rescue-clause/150624>\
**Category:** Ruby\
**Created:** [October 10, 2008, 3:53pm UTC](https://www.ruby-forum.com/t/rescue-clause/150624 "2008-10-10T15:53:33Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![oldbug](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/c0e974/32.png) [@oldbug](https://www.ruby-forum.com/u/oldbug)\
**Post date:** [October 10, 2008, 3:53pm UTC](https://www.ruby-forum.com/t/rescue-clause/150624/1 "2008-10-10T15:53:33Z")

</div>

I have been looking at the source code for rake (as you can probably  
tell  
from my previous questions), in an attempt to study a reasonable sized  
Ruby  
application and see what I can learn from the exercise. I’ve come  
across  
something that looks like it could be an innocuous typo in the code, or  
it  
could be doing something that I just don’t understand. Here is the code  
snippet:

```
def standard_exception_handling
  begin
    yield
  rescue SystemExit => ex
    # Exit silently with current status
    exit(ex.status)
  rescue SystemExit, OptionParser::InvalidOption => ex
    # Exit silently
    exit(1)
  end
end

```

I am curious as to why SystemExit shows up in 2 different rescue  
clauses.  
Is that a typo? Or is something else going on?

–wpd

---

<div class="post-metadata">

**Author:** ![oldbug](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/c0e974/32.png) [@oldbug](https://www.ruby-forum.com/u/oldbug)\
**Post date:** [October 10, 2008, 5:06pm UTC](https://www.ruby-forum.com/t/rescue-clause/150624/2 "2008-10-10T17:06:25Z")

</div>

The difference seems to be in that ’ OptionParser::InvalidOption ’ token  
but it’s the first time I saw a begin-rescue block of this kind.

---

<div class="post-metadata">

**Author:** ![oldbug](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/c0e974/32.png) [@oldbug](https://www.ruby-forum.com/u/oldbug)\
**Post date:** [October 10, 2008, 5:26pm UTC](https://www.ruby-forum.com/t/rescue-clause/150624/3 "2008-10-10T17:26:57Z")

</div>

2008/10/10 Patrick D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> ```
> rescue SystemExit => ex
> # Exit silently with current status
> exit(ex.status)
> rescue SystemExit, OptionParser::InvalidOption => ex
> # Exit silently
> exit(1)
> end
> 
> ```
> 
> end
> 
> I am curious as to why SystemExit shows up in 2 different rescue clauses.  
> Is that a typo? Or is something else going on?

The the first rescue clause and the SystemExit in the second clause  
can be removed without changing the semantics of the code.

As a sidenote, something being popular does not necessarily  
mean it should be used as a model for good Ruby code.  
Sometimes the techniques used only make sense in a  
historical context.

Stefan

---

<div class="post-metadata">

**Author:** ![oldbug](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/o/c0e974/32.png) [@oldbug](https://www.ruby-forum.com/u/oldbug)\
**Post date:** [October 10, 2008, 5:46pm UTC](https://www.ruby-forum.com/t/rescue-clause/150624/4 "2008-10-10T17:46:17Z")

</div>

> Stefan
> 
> In order to shorten my email, I left out the rest of the code, which reads:

```
  rescue Exception => ex
    # Exit with error message
    $stderr.puts "rake aborted!"
    $stderr.puts ex.message
    if options.trace
      $stderr.puts ex.backtrace.join("\n")
    else
      $stderr.puts ex.backtrace.find {|str| str =~ /#{@rakefile}/ } 

```

||  
“”  
$stderr.puts “(See full trace by running task with --trace)”  
end  
exit(1)

Because the code continues on to rescue Exception (which is the ancestor  
of  
all exceptions), the code does need to rescue SystemExit separately (and  
before, I believe) Exception.

Is there a historical reason why the second rescue clause contains  
SystemExit and OptionParser::InvalidOption. I understand your point  
about  
what makes a good model for Ruby code. In my case, having used  
makefiles  
for decades, and having been quite comfortable with them (most of the  
time),  
I am looking at rake and saying “what’s in it for me?” So far, the  
answer  
has been, “Oh, that’s cool! This feature and that feature certainly  
would  
make my life easier. Hmmm… I wonder how (s)he did that?” at which  
point  
I start to explore.

Having the historical “proto\_rake.rb” file and seeing the power of that  
simple script, and seeing to where it has evolved at this point in time,  
is  
also educational.

–wpd