Respected monks,

May be I am getting confused and/or doing something stupid, but please help me understand this.

I am trying to change the array content. So I wrote the following. 

use strict;
use warnings;

my @arr = (1..10);

sub test_this {
    print "Inside the sub, before the map \@arr: @arr\n";
    print "Inside the sub, before the map \@\_ = @_\n";
    @arr = map { 2 * $_ } @_;
    print "Inside the sub, after the map \@arr: @arr\n";
    print "Inside the sub, after the map \@\_ = @_\n";
}
print "Before calling the sub test_this \@arr: @arr\n";
&test_this(@arr);
print "After calling the sub test_this \@arr: @arr\n";

[download]

But it seems to alter the @_ as well after the map. Here's the output.

pritesh@t430:~$ perl test.pl 
Before calling the sub test_this @arr: 1 2 3 4 5 6 7 8 9 10
Inside the sub, before the map @arr: 1 2 3 4 5 6 7 8 9 10
Inside the sub, before the map @_ = 1 2 3 4 5 6 7 8 9 10
Inside the sub, after the map @arr: 2 4 6 8 10 12 14 16 18 20
Inside the sub, after the map @_ = 2 4 6 8 10 12 14 16 18 20
After calling the sub test_this @arr: 2 4 6 8 10 12 14 16 18 20
pritesh@t430:~$

[download]

I was not expecting the @_ to change after the map and was expecting Inside the sub, after the map @_ =  1 2 3 4 5 6 7 8 9 10 but what shows is  Inside the sub, after the map @_ = 2 4 6 8 10 12 14 16 18 20

First I thought @_ is a copy of whatever I pass to the sub. But that's not the case.

What am I missing?

In reply to How come @_ gets changed here? by pritesh_ugrankar

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