cell ( identifier ) {
  keyword2 { };
  ...
  keyword3 { keyword4 {  } };
}

...more sections...

#!/usr/bin/perl -w

use strict;

my $input_file = "input";
open FILE, "<$input_file" or die $!;

my $in_block = 0;
my $current_block = '';
my $open_bracket_count = 0;
while( my $line = <FILE> ) {
    if ( $line =~ /cell/ ) {
    	$in_block = 1;
    }

    if ( $in_block ) {
    	while ( $line =~ /([{}]{1})/g ) {
    		my $token = $1;
    		if ( $token eq '{' ) {
    			$open_bracket_count++;
    		} elsif ( $token eq '}' ) {
    			$open_bracket_count--;
    		}
    	}

    	$current_block .= $line;
    }

    if ( $open_bracket_count == 0 && $current_block ne '' ) {
    	print '-' x 80, "n";
    	print $current_block, "n";
    	$in_block = 0;
    	$current_block = '';
    }
}
close FILE or die $!;