Some changes to your code to make it clearer!

use strict;
use warnings;
 
my $n="outer";
 
my $f;
 
{
  my $n="ok";
  $f=sub { eval "".shift };
  check();               #  "ok"
};
 
sub check {
  print $f->('$n')
}
 
print $n;                   # "outer"
 
exit;
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