This works for me. See also How to ask better questions using Test::More and sample data.

use strict;
use warnings;

use Test::More tests => 2;

my $in = <<EOT;
ASDF {
    tmp
    foo_match
    tmp
}
string2 {
    tmp
}
string3 {
    tmp
    bar_match
    tmp
}
EOT

my $re = '^ASDF {[^{]*foo_match[^}]*}';

like $in, qr/$re/m, 'foo_match found in ASDF';
$re =~ s/foo/bar/;
unlike $in, qr/$re/m, 'bar_match not found in ASDF although present in
+ string3';
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