Forum: Ruby $0 is truncated

If I assign a new value to $0, I find it is truncated.

$ cat test-dollar0.rb
puts $0
str = "/foo" * 20
puts str.size
$0 = str
puts $0
puts $0.size

$ ruby test-dollar0.rb
test-dollar0.rb
80
/foo/foo/foo/foo/foo
20

$ ln -s test-dollar0.rb td.rb
$ ruby td.rb
td.rb
80
/foo/foo/f
10

In 1.8.6 I can get around this by $0.replace('....'), which sets $0 to
any string I like. However this doesn't work in 1.8.7 or 1.9, because in
those versions $0 is a frozen string.

Any suggestions for how to fix this? The application is that I want to
start launcher program A, which in turn loads program B. Program B may
be a Test::Unit test suite, and Test::Unit gets the test suite name from
$0. So I either end up with the test suite having the name of program A
(which is wrong), or a truncated version of program B's name (which is
also wrong)

Thanks,

Brian.

On 16.05.2009 15:03, Brian Candler wrote:
> $ ruby test-dollar0.rb
> 10
> also wrong)
Modifying $0 seems a bit hackish to me.  Can't you just set the name
explicitly?

Kind regards

  robert

On May 16, 2009, at 6:03, Brian Candler <b.candler@pobox.com> wrote:

> If I assign a new value to $0, I find it is truncated.

This behavior is OS dependent, try a different OS.

Hi,

In message "Re: $0 is truncated"
    on Sat, 16 May 2009 22:03:36 +0900, Brian Candler 
<b.candler@pobox.com> writes:

|If I assign a new value to $0, I find it is truncated.

Platform info please.  On some platforms, changing program name (as
seen from ps for example) is limited to the original size.  We cannot
relax OS limitation.

              matz.

Yukihiro Matsumoto wrote:
> Hi,
> 
> In message "Re: $0 is truncated"
>     on Sat, 16 May 2009 22:03:36 +0900, Brian Candler 
> <b.candler@pobox.com> writes:
> 
> |If I assign a new value to $0, I find it is truncated.
> 
> Platform info please.  On some platforms, changing program name (as
> seen from ps for example) is limited to the original size.  We cannot
> relax OS limitation.

This is under Linux (Ubuntu Hardy).

Yes, I'm aware that maybe setproctitle has limits, but it's also useful 
to set $0 to a longer Ruby string (even if that's not fully reflecting 
in the proctitle), because another piece of Ruby code in the same 
process may be testing the value of $0.

In ruby 1.8.6, I can use $0.replace("any long string") which works just 
fine for setting $0 - presumably not setting the proctitle of course. 
But this stopped working in 1.8.7/1.9 because $0 is frozen.

Regards,

Brian.

Hi,

In message "Re: $0 is truncated"
    on Sun, 17 May 2009 02:22:45 +0900, Brian Candler 
<b.candler@pobox.com> writes:

|This is under Linux (Ubuntu Hardy).
|
|Yes, I'm aware that maybe setproctitle has limits, but it's also useful 
|to set $0 to a longer Ruby string (even if that's not fully reflecting 
|in the proctitle), because another piece of Ruby code in the same 
|process may be testing the value of $0.
|
|In ruby 1.8.6, I can use $0.replace("any long string") which works just 
|fine for setting $0 - presumably not setting the proctitle of course. 
|But this stopped working in 1.8.7/1.9 because $0 is frozen.

OK, choose either from the following.

  [ ] it's OK (for you) that $0 is not corresponding to process name
      read by ps etc. at all, i.e. if you set $0 longer than the
      limit, $0 will be updated but the proc title will not.

  [ ] it's OK (for you) that $0 is not always corresponding to process
      name read by ps etc.; in this case if you set $0 longer than the
      limit, $0 will be updated but the proc title will be truncated to
      the limit.

  [ ] it's important for you to just update the $0, so that $0 string
      should not be frozen to allow replacing.  When you replace $0
      string, you'd take the responsibility.

              matz.

Yukihiro Matsumoto wrote:
>   [ ] it's OK (for you) that $0 is not always corresponding to process
>       name read by ps etc.; in this case if you set $0 longer than the
>       limit, $0 will be updated but the proc title will be truncated to
>       the limit.

Yes, that would be my preferred option.

I don't mind whether $0 is frozen. Actually, I wrote $0 = ... 
originally, and only changed it to $0.replace(...) as a workaround.

Regards,

Brian.

On May 16, 2009, at 13:36, Brian Candler <b.candler@pobox.com> wrote:

> originally, and only changed it to $0.replace(...) as a workaround.
In this case, why is it important that you check $0? Why not use any
other global variable?

On May 16, 6:24 pm, Eric Hodel <drbr...@segment7.net> wrote:
> In this case, why is it important that you check $0? Why not use any  
> other global variable?

I'm guessing it has to do with the bit in the original post where he
said "Test::Unit gets the test suite name from $0".

Hi,

At Sun, 17 May 2009 05:36:39 +0900,
Brian Candler wrote in [ruby-talk:336729]:
> I don't mind whether $0 is frozen. Actually, I wrote $0 = ... 
> originally, and only changed it to $0.replace(...) as a workaround.

You can find a hint in ext/extmk.rb.

  $progname = $0
  alias $PROGRAM_NAME $0
  alias $0 $progname

  trace_var(:$0) {|val| $PROGRAM_NAME = val} # update for ps

Nobuyoshi Nakada wrote:
> Hi,
> 
> At Sun, 17 May 2009 05:36:39 +0900,
> Brian Candler wrote in [ruby-talk:336729]:
>> I don't mind whether $0 is frozen. Actually, I wrote $0 = ... 
>> originally, and only changed it to $0.replace(...) as a workaround.
> 
> You can find a hint in ext/extmk.rb.
> 
>   $progname = $0
>   alias $PROGRAM_NAME $0
>   alias $0 $progname
> 
>   trace_var(:$0) {|val| $PROGRAM_NAME = val} # update for ps

Wow, that's a trick I wouldn't have thought of in a hundred years :-) 
Thank you.