Re-reading what you say you want, this seems to meet all your requirements:

my (@a, @b, @c, @d); # create and populate arrays

#Define a "Mapping hash":
my %aref = (a=>@\a,  b=>\@b,  c=>\@c,  d=>\@d  );
 # (Same as toolc's solution)
my $x = "b"; # I want to access "@b"

my $extracted_value_5_from_b = $aref{ $x }->[5];
my @entire_array_b_copy = @{ $aref{ $x } };

# Alternative, closer to the syntax you seek..
my $y = $aref{ b };

for ( @$y ){
  # We are iterating through @b here ...
}

#-- Strict-compliant, maintainable version ...
my $z=\@b;
for ( @$z ){
  # We are iterating through @b here ...
}
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