Truncating string set on $0

Hi,

I have a "pre-ruby-launcher", which loads some environment
variables and launches the other script. That is, the first script
is just temporary, while the second script is the final (main) one.

To make it work transparently, I used to set the $0 variable to
the filename of the second script, and everything, for months,
ran smoothly. That is, until today. Today I noticed that a large
filename string could be truncated, and it seems that the length
depends on the initial command for launching Ruby.

For example, running this script:
s = 'a'
100.times{|n|
  z = s * n
  $0 = z
  if z.size != $0.size
    p n
    exit
  end
}

Prints:
dewd@corvina:~/t_/tempo$ ruby first_file.rb
19

It stops at the length of "ruby first_file.rb".

Thankfully, despite this issue, things have worked ok
until today.

I'm not sure you want to fix this or whether this is
could be considered a problem at all. I can circumvent
this issue at least for my latest usage of this.

Cheers,
Joao