From: Rudolf Polzer <denshimeiru-sapmctacher@...>
Date: 2003-04-21T05:03:16+09:00
Subject: Re: Multi-Lingual Ruby

Scripsit ille �Tim Heaney� <heaney@cablespeed.com>:
> Ryan Pavlik <rpav@nwlink.com> writes:
> > 
> > The question is why this influences ruby...
> 
> In the Perl documentation, it says
> 
>        If the #! line does not contain the word "perl", the pro-
>        gram named after the #! is executed instead of the Perl
>        interpreter.  This is slightly bizarre, but it helps peo-
>        ple on machines that don't do #!, because they can tell a
>        program that their SHELL is /usr/bin/perl, and Perl will
>        then dispatch the program to the correct interpreter for
>        them.
> 
> Perhaps Matz reasoned similarly for Ruby.

But it's implemented differently.

  rpolzer@katsuragi tmp $ ls -l r
  lrwxrwxrwx    1 rpolzer  users          13 2003-04-20 21:35 r -> /usr/bin/ruby

  rpolzer@katsuragi tmp $ cat test
  #!/tmp/r
  print "Hello\n"

  rpolzer@katsuragi tmp $ ruby test
  test:1: Can't exec /tmp/r (fatal)

That took very LONG - and the reason:

  rpolzer@katsuragi tmp $ strace ruby test 2>&1 |grep ^exec
  execve("/usr/bin/ruby", ["ruby", "test"], [/* 62 vars */]) = 0
  execve("/tmp/r", ["/tmp/r", "test"], [/* 62 vars */]) = 0
  execve("/tmp/r", ["/tmp/r", "test"], [/* 62 vars */]) = 0
  execve("/tmp/r", ["/tmp/r", "test"], [/* 62 vars */]) = 0
  execve("/tmp/r", ["/tmp/r", "test"], [/* 62 vars */]) = 0
  execve("/tmp/r", ["/tmp/r", "test"], [/* 62 vars */]) = 0
  execve("/tmp/r", ["/tmp/r", "test"], [/* 62 vars */]) = 0
  execve("/tmp/r", ["/tmp/r", "test"], [/* 62 vars */]) = 0
  execve("/tmp/r", ["/tmp/r", "test"], [/* 62 vars */]) = 0
  execve("/tmp/r", ["/tmp/r", "test"], [/* 62 vars */]) = 0
  [...]
  execve("/tmp/r", ["/tmp/r", "test"], [/* 62 vars */]) = 0
  execve("/tmp/r", ["/tmp/r", "test"], [/* 62 vars */]) = -1 EMFILE (Too many open files)

Perl, contrary, doesn't do that with a similar setup:

  execve("/usr/bin/perl", ["perl", "test"], [/* 62 vars */]) = 0
  execve("/tmp/p", ["/tmp/p", "test"], [/* 62 vars */]) = 0

and then happily runs the script. Probably it checks if the script
interpreter names match (argv[0] and the #! line). I think it can be
shown like that:

  rpolzer@katsuragi tmp $ perl test
  Can't exec /tmp/pa at test line 1.

but

  rpolzer@katsuragi tmp $ ./p test
  Hello

while ./p is symlinked to /usr/bin/perl. Why? #!/tmp/pa contains the
substring 'p'...



-- 
> Hatte ~1a lang $NONAMELAPTOP als Arbeitsplatz, der wurde
> auch recht warm. Einmal so warm, da� [...] das Display einfror [...]
Das verletzt den zweiten Hauptsatz der Thermodynamik.
                                  [Sebastian Posner und Stefan Froehlich in dasr]