use strict; use warnings; my $str = 'MKTVEQTSPTMTSEKARWIYQKMVEIRMFEDRVHDIFSKGEIPGFVHLYAGEEAIAVGLCAHLDHNDYITSTHRGHGHCIAKGCELDGMMAEIYGKSTGLCKGKGGSMHIADLDRGMLGANGIVGGGFTLAAGAALTAKFKQTGGVAVCFFGDGANNQGTFHEGINLAAIWDLPVVFVAENNGYGEATPFHYASACEQITDRAKGYNIPGVKVDGKDVVAVYEVAREAVERARRGEGPTLIECITYRNYGHFEGDAQTYKTGREKEEHTEERDAITLFEKYALSNNLLTEEAIQTVRHEVEQSVDRAVDFANASDYPQPEELLTDVYVSYDHEGRNG'; $str =~ s/(.{10})/$1 /gsi; $str =~ s/((?:[^ ]+ ){5})/$1\n/gsi; print $str;