What you say does not agree to the docs and to my practice.

 $ cat whichperl.pl
#!/usr/bin/perl

printf "operating system: %s\n executable: %s\n", $^O,  $^X, ;
[download]

And see the results:

 
$ perl whichperl.pl
operating system: linux
 executable: /usr/bin/perl
 
$ chmod +x whichperl.pl
$ ./whichperl.pl
 operating system: linux
 executable: /usr/bin/perl
[download]

And later, to another OS:

$ perl whichperl.pl
 operating system: freebsd
 executable: /usr/local/bin/perl
[download]