From: nobu.nokada@...
Date: 2003-12-18T17:39:27+09:00
Subject: Re: setting $0

Hi,

At Thu, 18 Dec 2003 15:32:38 +0900,
Zach Chinnery wrote:
> When the $0 object is first created it has a length that is correct for the
> length of the filename. You can check the length with '$0.length' - for a
> file called t.rb the length is 9, for a file called trb.rb it is 11, and so
> on. Not sure why it seems to be longer than the actual filename.

It icnludes also arguments, and the interpreter name length.

> When you assign a string to $0 within your code it seems that it is only
> storing (or displaying...?) the number of characters corresponding to the
> length of the filename.
> 
> So if your file is called t.rb you will see 'My Applic'.
>    if your file is called tr.rb you will see 'My applica'.
>    if your file is called reallylongname.rb you will see the entire string.
> 
> Not sure if this is a bug or expected behaviour...I guess that $0 should be
> kept for holding the filename, and not later assigned with anything else...

Feature, to change command line shown by ps.

$ ruby -e '$0 = "Sleeping...zzz"; sleep' &
[1] 5349
$ ps $!
  PID TTY      STAT   TIME COMMAND
 5349 pts/4    S      0:00 Sleeping...zzz

If you want change $0 value inside a script (without ps), alias
it.  You can see an example in ext/extmk.rb.

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

-- 
Nobu Nakada