#!/bin/cat

# Author: Hugh Sasse <hgs@dmu.ac.uk>
# Data: 17-AUG-2000

# Ruby can make really intelligent use of the #! line, as this
# session within a C Shell (/bin/csh) shows:

brains hgs 36 %> chmod u+x !$
chmod u+x ./t.rb
brains hgs 37 %> !.
./t.rb
solaris
brains hgs 38 %> ruby !$
ruby ./t.rb
solaris
brains hgs 39 %> ksh
$ ./t.rb
solaris
$ exit
brains hgs 40 %> sh
$ ./t.rb
solaris
$ exit
brains hgs 41 %> sh t.rb
t.rb: print: not found
t.rb: O,: not found
brains hgs 42 %> ksh t.rb
$^O, 

brains hgs 43 %> python t.rb 
  File "t.rb", line 2
    print $^O, "\n";
          ^
SyntaxError: invalid syntax
brains hgs 44 %> csh t.rb
Variable syntax

No point in testing this on perl, it is already a perl program.
We can test perl being passed a ruby program:

brains hgs 57 %> perl self_print
#!/usr/local/bin/ruby
DATA.rewind
print DATA.readlines
__END__
brains hgs 58 %> 

This is with Python 1.5.1 , Ruby 1.4.4, Perl 5.005_03