from perlsub, The array @_ is a local array, but its elements are aliases for the actual scalar parameters. In particular, if an element $_[0] is updated, the corresponding argument is updated, but below code block output are not expected, why? 

sub swap_1 { (@_) = reverse(@_); }

sub swap_2 { 
    
    my @item = reverse(@_);
    
    (@_) = ($item[0], $item[1]); 
    
    print "##swap2_1: $item[0]\n";
    print "##swap2_1: $item[1]\n";
    print "-------------\n";
    
    $_[0] = $item[0];
    $_[1] = $item[1];
    
    print "##swap2_2: $_[0]\n";
    print "##swap2_2: $_[1]\n";
    print "-------------\n";    
    
}

sub swap_3 { 
    $_[0] = "AAA";
    $_[1] = "BBB";
}

my $one = "I am one";
my $two = "I am two";
swap_1($one,$two);
print "one is '$one'\n";
print "two is '$two'\n";
print "-------------\n";
swap_2($one,$two);
print "one is '$one'\n";
print "two is '$two'\n";
print "-------------\n";
swap_3($one,$two);
print "one is '$one'\n";
print "two is '$two'\n";
print "-------------\n";

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I expect swap_1, swap_2 can do the swap work, but obviously, I am wrong. but swap_3 is expected

below are the output 

one is 'I am one'
two is 'I am two'
-------------
##swap2_1: I am two
##swap2_1: I am one
-------------
##swap2_2: I am two
##swap2_2: I am one
-------------
one is 'I am one'
two is 'I am two'
-------------
one is 'AAA'
two is 'BBB'
-------------

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In reply to Accessing Arguments inside Subroutines via @_ by citi2015

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