Nested #! interpreters

Neutron Jack has asked for the wisdom of the Perl Monks concerning the following question:

I have two scripts, alpha and beta:

alpha:

#! /tmp/beta
12345
abcde
[download]

beta:

#! /usr/bin/perl -wln
print scalar reverse if $. > 1;
[download]

(The real beta is much more complex.) I hoped that alpha would print:

    54321
    edcba
[download]

What actually printed:

    ./alpha: line 2: 12345: command not found
    ./alpha: line 3: abcde: command not found
[download]

"man execve" says that you can't have an interpreter running an interpreter, at least on Red Hat:

execve() executes the program pointed to by filename. filename must be either a binary executable, or a script starting with a line of the form "#! interpreter [arg]". In the latter case, the interpreter must be a valid pathname for an executable which is not itself a script,

It seems that Perl was invoked with alpha as an argument, noticed that the #! line didn't mention perl, and helpfully invoked a shell to interpret alpha. Well, heck—what can I do? I want alpha to remain unchanged. Am I forced to write beta in a compiled language? I want to use Perl, of course!

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Re: Nested #! interpreters by chromatic (Archbishop) on Feb 21, 2004 at 20:05 UTC
`system( '/path/to/beta', '/path/to/alpha' ) == 0 or die "Cannot beta alpha: $?\n";` [download] If you're really paranoid, use `$^X` as the first argument to system.	[reply] [d/l] [select]
•Re: Nested #! interpreters by merlyn (Sage) on Feb 21, 2004 at 22:03 UTC
Since a PAR executable is a proper executable, you could always do one of those. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply]
Re: Nested #! interpreters by ambrus (Abbot) on Feb 21, 2004 at 20:42 UTC
As another solution, just write a c program that execs perl /tmp/beta (and passes any command line arguments it got), and then use that as an interpreter in alpha.	[reply]
Re: Nested #! interpreters by flyingmoose (Priest) on Feb 21, 2004 at 21:49 UTC
Isn't shell piping the proper thing to use here?	[reply]