[pgh-pm] More shebang fun

[Tom Moertel]

Perl mongers,

Inspired by Casey's hackrifficly splendid talk tonight, I hacked up the 
following alternative method for using shebang notation to run scripts 
that are written in Perl-based languages.  The idea is to minimize the 
amount of work that we must do in C by immediately handing off to a 
Perl-based handler.

The C program is tiny:

     #include <stdlib.h>
     #include <string.h>
     #include <errno.h>

     int main(int argc, char* argv[]) {
         char* cmd = malloc(strlen(argv[0]) + 4);
         strcat(strcpy(cmd, argv[0]), ".pl");
         execv(cmd, argv);
         perror("exec");  /* shouldn't get here */
         return 1;
     }

The C program retrieves the pathname under which it was invoked, appends 
a ".pl" suffix to it, and then hands off to that program.

To use the program, we create a script handler in Perl.  It runs the 
actual scripts, which it receives via its first argument.  Then we 
create a symlink from the C program to the script handler, but leaving 
off the handler's ".pl" suffix.  When we write scripts in our scripting 
language, we place the path to the handler -- again minus the ".pl" 
suffix -- in their shebang section.  That's it.

When we run a script, here's what happens.  First, the shell finds the 
shebang section of the script, which points to the symlink, and executes 
it, thereby invoking the C program.  The C program tacks a ".pl" suffix 
onto the name under which it was invoked and executes that program, 
thereby handing off to our Perl-based script handler.  The handler 
receives the path to our original script as its first argument and runs 
the script.

The enclosed script shows how it all works.  When the script is done, 
you can "cd /tmp/shebanger" to examine the setup more closely.

Cheers,
Tom
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