use strict;

my %numbers;

while (<DATA>) {
	$numbers{$1}++ if /^(\d+)/;
}

print "$_\n" foreach keys %numbers;

__DATA__
123askdjha
1ad
asldhasd
asdklsd123
10
2fer

##</code><code>##

1
2
10
123

##</code><code>##

use strict;

my @numbers;

while (<DATA>) {
	/^(\d+)/;
	push(@numbers, $1) unless grep(/^$1$/, @numbers) || $1 eq '';
}

print "$_\n" foreach @numbers;

__DATA__
123askdjha
1ad
asldhasd
asdklsd123
10
2fer

##</code><code>##

123
1
10
2