use warnings;
use strict;

my $thing = 123;

{
    my $thing = 456;
}

print $thing; # 123

open my $fh, '<', 'file.txt' or die $!;

{
    local $/; # slurp in a file
    my $contents = <$fh>
    ...
}

# now we go back to reading a file line-by-line again

while (<$fh>){
   ...
}

##</code><code>##

my @list = map {$_ => 1} @other_list;
my @filtered_list = grep {$_ =~ /blah/} @some_list;