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comp.lang.ruby

getting rid of $0

Michel Demazure

7/2/2007 6:00:00 PM

The common idiom
if __FILE__ == $0 then ...
gives bugs when $0 is not what one would expect, for instance under a
debugger, or in rubyscript2exe, etc.

There should be a primitive test
if <nice name to be found> then...

--
Posted via http://www.ruby-....
6 Answers

Tim Pease

7/2/2007 6:10:00 PM

0

On 7/2/07, Michel Demazure <michel@demazure.com> wrote:
> The common idiom
> if __FILE__ == $0 then ...
> gives bugs when $0 is not what one would expect, for instance under a
> debugger, or in rubyscript2exe, etc.
>
> There should be a primitive test
> if <nice name to be found> then...
>

require 'English'

if __FILE__ == $PROGRAM_NAME
...
end


Blessings,
TwP

Alex Young

7/2/2007 6:11:00 PM

0

Tim Pease wrote:
> On 7/2/07, Michel Demazure <michel@demazure.com> wrote:
>> The common idiom
>> if __FILE__ == $0 then ...
>> gives bugs when $0 is not what one would expect, for instance under a
>> debugger, or in rubyscript2exe, etc.
>>
>> There should be a primitive test
>> if <nice name to be found> then...
>>
>
> require 'English'
>
> if __FILE__ == $PROGRAM_NAME
> ...
> end
>
Does that solve the problem? Isn't that vulnerable to the same issues
as just using $0?

--
Alex

Tim Pease

7/2/2007 6:22:00 PM

0

On 7/2/07, Alex Young <alex@blackkettle.org> wrote:
> Tim Pease wrote:
> > On 7/2/07, Michel Demazure <michel@demazure.com> wrote:
> >> The common idiom
> >> if __FILE__ == $0 then ...
> >> gives bugs when $0 is not what one would expect, for instance under a
> >> debugger, or in rubyscript2exe, etc.
> >>
> >> There should be a primitive test
> >> if <nice name to be found> then...
> >>
> >
> > require 'English'
> >
> > if __FILE__ == $PROGRAM_NAME
> > ...
> > end
> >
> Does that solve the problem? Isn't that vulnerable to the same issues
> as just using $0?
>

You're correct! That does not solve the problem. :/

Hmmm ... the solution I use most often is to have a top-level function
that runs the application. This top-level function is called by a
separate Ruby script.


class MyApp
def self.run( args )
new(args).run
end
...
end

And in an executable file called "my_app"

#!/usr/bin/env ruby

require 'MyApp'
MyApp.run ARGV


I try to avoid the __FILE__ == $0 idiom when I distribute code. You
run into the problems the original poster pointed out, and rubygems
also wrappers up all your executables with it's own special calling
semantics (provides compatibility between windows / *nix).

Not the answer you want to hear, but, "don't do that". Sorry :/

TwP

Ryan Davis

7/2/2007 8:47:00 PM

0


On Jul 2, 2007, at 11:11 , Alex Young wrote:

> Tim Pease wrote:
>> On 7/2/07, Michel Demazure <michel@demazure.com> wrote:
>>> The common idiom
>>> if __FILE__ == $0 then ...
>>> gives bugs when $0 is not what one would expect, for instance
>>> under a
>>> debugger, or in rubyscript2exe, etc.
>> require 'English'
>> if __FILE__ == $PROGRAM_NAME
> Does that solve the problem? Isn't that vulnerable to the same
> issues as just using $0?

Solve what problem? The code is doing what you asked it to do, that
isn't a problem, that's programming.

The code clearly reads "if this file is the program" which is NOT the
case when run under a debugger. I'm not sure what rubyscript2exe
generates, but my guess is that can be solved on their end somehow. I
generally don't want that code to run when I'm poking around in a
debugger or something similar. If I do, I set the values inside the
debugger and don't worry about it.

Jano Svitok

7/2/2007 9:03:00 PM

0

On 7/2/07, Michel Demazure <michel@demazure.com> wrote:
> The common idiom
> if __FILE__ == $0 then ...
> gives bugs when $0 is not what one would expect, for instance under a
> debugger, or in rubyscript2exe, etc.
>
> There should be a primitive test
> if <nice name to be found> then...

rcov provides for this case a special switch --replace-progname that
does what the name says. Unfortunately, sometimes there's still a
mismatch between those two:
one is ./something.rb while the other is just something.rb. Therefore
I use the following variation of the idiom (I haven't checked this
under debugger or any other prog):

if File.expand_path(__FILE__)==File.expand_path($0)

I have posted a patch for ruby-prof that adds a similar switch and it
has been accepted.

Anyway, $0 seems to be a normal variable that you can set to anything
you want, so creating a small wrapper script should not be a problem.
E.g.

$0 = ARGV.shift
require $0

ara.t.howard

7/3/2007 6:43:00 AM

0


On Jul 2, 2007, at 3:03 PM, Jano Svitok wrote:

> Anyway, $0 seems to be a normal variable that you can set to anything
> you want, so creating a small wrapper script should not be a problem.
> E.g.
>
> $0 = ARGV.shift
> require $0


be careful, $0 is not a normal variable:

cfp:~ > cat a.rb
$0 = 'foobar'

puts `ps wwwaux|grep foobar`


cfp:~ > ruby a.rb
ahoward 10371 2.6 -0.1 29204 1388 p2 S+ 12:41AM 0:00.01
foobar
ahoward 10372 1.4 -0.0 27728 584 p2 S+ 12:41AM 0:00.00
sh -c ps wwwaux|grep foobar
ahoward 10374 1.2 -0.0 27368 448 p2 S+ 12:41AM 0:00.00
grep foobar


it actually assigns to c's argv


-a
--
we can deny everything, except that we have the possibility of being
better. simply reflect on that.
h.h. the 14th dalai lama