use strict;
my @fileone = qw/ 123456 123457 123458/;

while (my $line = <DATA>) {
  foreach my $pattern(@fileone) {
    if ($line =~ /^$pattern/) {print $line."\n";}
  }
}

__DATA__
123456 foo
123456 bar
123457 foobar
123455 this wouldn't be printed to new file