#!/usr/bin/perl

use strict;
use warnings;
use File::Find::Rule;

my $file  = 'bigfile.txt';
my @files = File::Find::Rule
	->file()
	->name( qr/^\d+-$file\Z/)
	->in( '.' )
;

open OUT, '>', "new_$file" or die $!;
for (sort @files) {
	open IN, $_;
	print OUT while <IN>;
}