The expression qw(@hash_tags) does not interpolate an array variable, it merely returns the literal string '@hash_tags'. I think you want:

@USERlist = @hash_tags;
...
@STATIClist = @tags;
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and the code should work as expected.

Update: See Quote and Quote like Operators.

Hope that helps,

See qw: The above expression won't interpolate the array. In order to take a reference to @hash_tags, you already have the correct syntax:

Just replace \@USERlist, \@STATIClist with \@hash_tags, \@tags. Since you're not modifying the original arrays, there is no need to make a copy, so just put the original arrays in your print statements as well, such as:

You want to know which entries are in both lists:

my %matched;
@matched{@STATIClist} = ();

print "Valid tags:\n";
print "\t$_\n" for grep { exists $matched{$_} } @USERlist;
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If you want to store the list...:

my @valid_tag = grep { exists $matched{$_} } @USERlist;
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What about good old hash functions?

use Data::Dumper
my(@list_a)=(qw(a b c d e f g));
my(@list_b)=(qw(a c e g h j k));
my(%just_a,%just_b,%both);

@just_a{@list_a}=(); delete @just_a{@list_b};

@just_b{@list_b}=(); delete @just_b{@list_a};

@both{@list_a}=(); delete @both{keys %just_a};

print Data::Dumper->Dump([
      [keys %just_a],[keys %just_b],[keys %both]
  ],
  [qw/just_a just_b both/]
)
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Output:

$just_a = [
            'b',
            'd',
            'f'
          ];
$just_b = [
            'k',
            'h',
            'j'
          ];
$both = [
          'e',
          'c',
          'a',
          'g'
        ];
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---

s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e

Mis-interpreted question. However, THERE IS A BETTER WAY:

Search for an answer -- that's probably going to be quicker than asking and waiting for an answer. This is almost a FAQ and definitely can be found with minimal effort on this site.

Super Search or Google site:perlmonks.org intersection arrays will offer ways to solve your problem without annoying the electrons and silicon by copying the arrays to lists.