One approach (of many):

use strict;
use warnings;

use Test::More tests => 1;

my $have = "foo}\n}";
my $re   = qr/}\n}/;

like $have, $re, 'Matched';
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Update: reduced the regex to make it even simpler.

i need to match "}\n}" (without quotes and newline as in real).

The regex to match "}\n}" is /}\n}/ (unless you're using m{}, in which case you need to write m{\}\n\}}). Since that's pretty obvious, I wonder if maybe you're having problems with some of your code? If that's the case, maybe you could show the code you're having problems with in the form of a Short, Self-Contained, Correct Example: a short, runnable piece of code that reproduces the issue, short sample input, the expected output for that input, and the output you're getting instead, including any error messages (code and input/output in <code> tags).

Without more information, that regex would work. Is it perhaps there's whitespace you're not accounting for, since it looks like you're searching for braces that end a block?

If that's the case, I think you would want /}\n\w*}/ There's also a possibility you're editing a document from another filesystem, and newline is defaulting to your system. /}\n\r?}/ catches both Linux-y/Windows line endings.

whitespace you're not accounting for ... If that's the case, I think you would want /}\n\w*}/

That should probably be /}\n\s*}/, since \w means a word character.

/}\n\r?}/

That should probably be /}\r?\n}/, since \n\r would be LFCR (see also).

Thanks. I don't use regex too often anymore but I mostly remember it!