#!/usr/bin/perl 
 
print "Please type the file name of the protein sequence data: "; 
$proteinfilename = <STDIN>; 
chomp $proteinfilename; 
 
unless (open(PROTEINFILE, '<', $proteinfilename)){ 
    die "File \"$proteinfilename\" doesn\'t seem to exist!!\n"; 
} 
 
while(<PROTEINFILE>) { 
    next if(/^>/ or /^\s*$/); # skip empties and signature 
    chomp; # remove trailing newline 
    $seq .= $_; # accumulate lines in $seq 
} 
 
print "The aminoacid sequence $seq contains " 
.($seq =~ tr/F/F/)." Phenylalanine aminoacids\n";