use warnings;
use strict;

open my $fh,  '>', 'outfile3.txt' or die "can't open file: $!";
open my $fh2, '<', 'file1.txt'    or die "can't open file: $!";
while ( defined( my $line = <$fh2> ) ) {
    if ( $line =~ m{^(?<matched>.+?)\s+?.*?$}){
      print {$fh} $+{matched}, $/;
    }
}
close $fh2 or die "can't close file: $!";
close $fh  or die "can't close file: $!";