How about something like this:

$length determines the width of the column

undef $/;
my $sequence = <DATA>;
$sequence =~ s/\s+//g;
my $length = 60;


for ( my $pos = 0 ; $pos < length($sequence) ; $pos += $length ) {
    print substr($sequence, $pos, $length), "\n";
}


__DATA__
GAGGGTGCAATCTACAAGAGTGCGGGTTCGCGTTCAGTCCAAGCTGAACATAAACGCAAC
GCAAGGCCCCTCGACGCAGATACCGCGCTCAGGAGCATTCGAGAAGCCGAAGAAAATTCG
AAGACGAGGACCAGCTACACTGCGGACGGACTTCGGGCATGGAGGGCCAGTTCCAG

GTTGGCAAGGAGGAGGTCATCCAAGCATGGTACATGGACGACAGTGAAGAGGACCAGAGG
CTTCCTCATCATCGTGAGCCCAAAGAATTCATTCCTCTCGACAAACTTTCCG

AACTAGGAATATTAAGCTGGCGCCTAAATGCTGATGATTGGGAGAATGATGAGAACCTCA
AGAAAATTCGTGAAGCCAGGGGTTACTCTTACATG

GACATTTGTGATGTGTGCCCAGAGAAGTTGCCAAATTACGAGGCTAAGATAAAGAATTTC
TTTGAAGAACACTTGCATACTGATGAAGAGATACGATATTGCCTTGAGGGTAGCG

GCTACTTTGATGTGAGGGACCAAGATGATCAGTGGATCCGTGTAGCGGTAAAGAAAGGGG
GCATGATCGTTTTGCCTGCAGGAATGTATCATCGCTTTACGTTGGATAGTGACAACTACA
TCAAG

GCAATGCGTCTATTTGTGGGTGAGCCTGTCTGGACACCATACAATCGTCCGCATGACCAT
CTCCCGGCTAG
[download]