so shift physically removes the entry in @ARGV? this is interesting and i did not realize that

Indeed it does:

$ cat shifter.pl 
#!/usr/bin/env perl 
use strict;
use warnings;

do {
    print "ARGV is @ARGV\n";
    print "Shifting " . shift . " off ...\n";
} until $#ARGV < 0;

$ ./shifter.pl x y z
ARGV is x y z
Shifting x off ...
ARGV is y z
Shifting y off ...
ARGV is z
Shifting z off ...
$
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See perldoc -f shift for more.