note 2teez <p> Hi [serafinososi],<br><br> <i>...If the line starts with “>” (it is the first line of a FASTA file) the line is not considered...</i><br><br> What if the line that starts with ">" is more than one in the file what happens?<br><br> If I understand the OP's question, using the data provided, if I may suggest (adding to what others have said) using perl function [doc://split] may do like so: <c> use warnings; use strict; my $protein; while (<DATA>) { if (/^>/) { next; } else { $protein = join '', split; } } my $number_of_F = grep { /F/ } split //, $protein; print "The aminoacid sequence: ", $protein, " contains ", $number_of_F, " Phenylalanine aminoacids", $/; __DATA__ >gi|403369491|gb|EJY84591.1| Transcriptional regulator, Sir2 family protein Oxytricha trifallax MMKQLIKHNKNTPLFNFLRVKFSSTAATIQTQQTVNKPIESKFKEEKLDNYHDIYEKSKRLAEQISQSKS FICFTGAGLSTSTGIPDYRSTSNTLAQTGAGAYELEISEEDKKSKTRQIRSQVQRAKPSISHMALHALME NGYLKHLISQNTDGLHLKSGIPYQNLTELHGNTTVEYCKSCSKIYFRDFRCRSSEDPYHHLTGRQCEDLK CGGELADEIVHFGESIPKDKLVEALTAASQSDLCLTMGTSLRVKPANQIPIQTIKNKGQLAIVNLQYTPF DEIAQIRMHSFTDQVLEIVCQELNIKIPEYQMKRRIHIIRNAETNEIVVYGSYGNHKNIKLSFMQRMEYI DNKNHVYLALDKEPFHIIPDYFNFQNINTDQEEVEFRIHFYGHNSEPYFQLTLPRQSILELQAGEHLICD ITFDYDKLEWK </c> </p> <!-- Node text goes above. Div tags should contain sig only --> <div class="pmsig"><div class="pmsig-918402"> If you tell me, I'll forget.<br> If you show me, I'll remember.<br> if you involve me, I'll understand.<br> --- Author [unknown to me] </div></div> 1016025 1016025