#!/usr/bin/perl
use warnings;
use strict;

use Scalar::Util qw/ looks_like_number /;

my ( $file_in, $file_out ) = ( 'file1.txt', 'file2.txt' );

open my $IN,  '<', $file_in  or die "Cannot open '$file_in' because: $!";
open my $OUT, '>', $file_out or die "Cannot open '$file_out' because: $!";

while ( <$IN> ) {
    print $OUT join( "\t", grep looks_like_number( $_ ), split ), "\n";
    }

__END__