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

my @contigfile = qw( >37 ABC DEF GHI >456 JKL MNO PQR STU VWX YZ >38 );

my @result;
for my $i (0 .. $#contigfile) {
    my $current = $contigfile[$i];
    push @result, q() and next if 0 == index $current, '>';
    $result[-1] .= $current;
}

print "$_\n" for @result;