#!/usr/bin/perl -w

    use strict;

    my %hash;

    while (<DATA>) {
        chomp;
        next unless /\S/; # Skip blank lines
        /(\d+)/;          # Match the first number
        $hash{$1} = $_;
    }


    for my $key (sort {$a <=> $b} keys %hash) {
        print $key, "\t", $hash{$key}, "\n";
    }

    # Prints:

    # 1       1 2 3 4 5 
    # 10      10 20 30 40 50
    # 200     200 100 300 2 1

    __DATA__
    1 2 3 4 5 
    10 20 30 40 50
    200 100 300 2 1