#! perl

use strict;
use warnings;
use Data::Dump;

my   @matches;
push @matches, mysub($_) for <DATA>;
dd  \@matches;

sub mysub
{
    return shift =~ / > (\S+) \s /gx;
}

__DATA__
 
>NM_030643.4 Homo sapiens apolipoprotein L4 (APOL4) 
GAGGTGCTGGGGAGCAGCGTGTTTGCTGTGCTTGATTGTGAGCTGCTGGGAAGTTGTGACTTTCATTTTA
CCTTTCGAATTCCTGGGTATATCTTGGGGGCTGGAGGACGTGTCTGGTTATTATATAGGTGCACAGCTGG
>NM_001198855.1 Homo sapiens cytochrome P450 family 2 subfamily C member 8 (CYP2C8)
ACATGTCAAAGAGACACACAC
>NR_029834.1 Homo sapiens microRNA 200a (MIR200A), microRNA
CCGGGCCCCTGTGAGCATC
>AC067940.1 Homo sapiens clone RP11-818E9, LOW-PASS SEQUENCE SAMPLING
AAATACAACTTTAAATCAAAACGGTAAAAATTCCACTCTTTCATACTAACTTCAAAAGTATTTGCTTTAA
AAAAAAAGNNNNNNNNN