#!/usr/bin/perl -w 
use strict;

unless (open(F,'./your_file')){
	die "Unable to open file for reading $!";
}else{
	my $file_str = join("",<F>);
        close F;
	if($file_str =~ m/^(\.subckt.*?)x00/s){
                my $match_str = $1;
	        print $match_str."\n";
        }else{
                print "No match for you!";
        }
	exit;
}

__OUTPUT__
.subckt cct0 v0 v1 v2 v3
 
+ v4 v5 v6
 
* useless comment
+ v7 v8 v9
+ va vb