#!/usr/bin/perl
use warnings;
use strict;
use v5.10.0;

my $rx_consecutive = qr/
    ^ }
    (?:
        (?! ^ [{}] )
        .
    )*
    ^ }
/msx;

my @strings = split /!/, <<'STRINGS';
f()
{
    fred();
}

g()
{
    jim();
}
!
f()
{
    fred();
}

int i = 0;

}

g()
{
    jim();
}
!
f()
{
    if (i) {
        fred();
    }
}

g()
{
    jim();
}
STRINGS

for my $text (@strings) {
    say "Testing:\n$text\n";
    my $found = $text =~ $rx_consecutive;
    say "Double right-curly ", ($found? "found": "not found");
}
[download]