Getting rid of $0

Ruby
1

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 then…

2

On 7/2/07, Michel D. [email protected] 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 then…

require ‘English’

if FILE == $PROGRAM_NAME
…
end

Blessings,
TwP

3

Tim P. wrote:

require ‘English’

if FILE == $PROGRAM_NAME
…
end

Does that solve the problem? Isn’t that vulnerable to the same issues
as just using $0?

4

On 7/2/07, Alex Y. [email protected] wrote:

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. :confused:

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 :confused:

TwP

5

On 7/2/07, Michel D. [email protected] 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 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

6

On Jul 2, 2007, at 11:11 , Alex Y. wrote:

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.

7

On Jul 2, 2007, at 3:03 PM, Jano S. 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