#!/usr/bin/perl -w
use strict;
use autodie qw(open close); 

{ 
	undef $/; 
	my %file = ($1 => split /<\s*(.+)\n/ , <DATA>);
	
	map {
		$_ and open my $fh, q{>}, $_; select $fh;
		print $file{$_} and close;
	} keys %file;
}

__DATA__
< file1.txt
line1 of file1
line2 of file1
line3 of file1
line4 of file1
< file2.txt
line1 of file2
line2 of file2
line3 of file2
< file3.txt
line1 of file3
line2 of file3
line3 of file3
line4 of file3