These are indeed basic questions, as pointed out by stevieb. There are several ways to output to a file. Your operating system itself can probably do it with output redirection, or from within Perl, the open command can write to files instead of reading. Click on the links in the preceding sentence for more information and examples.

To put the outputs into bins for different string lengths, hashes are an excellent way to do that. I would use a hash of array refs. The perldata page is again another great documentation resource that will introduce you to the required concepts. The basic algorithm in your case would be to do everything you're already doing, but instead of displaying the "A" count and length with say, you would instead store it in a hash. The hash key would be the length, and the hash value would be an array ref.

Untested:

my $len = length;
$bins{$len} //= [ ];      # Set to blank array ref if not already set.
push @{$bins{$len}}, $a;  # Add $a to the array
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When it's all over, %bins (which you will of course need to declare before the main loop), has your A counts:

See sort for an explanation of how to sort your data.

for my $len (sort { $a <=> $b } keys %bins) {
    say "Length $len:";
    say for @{$bins{$_}};
}
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Some assembly and individual research required. :-)

Welcome davi54!

This site is about getting help for coding problems. Opening files, the question you just asked about is one of the most trivial and widely used pieces of functionality that any Perl programmer must learn early. Hint: once you get your file handle opened successfully, supply it to the print function before the information you want to print to it: print $fh "what I want to print to file\n";.

Please do some of your own homework, and give this part a try instead of having others write all of your code for you.

See open.

For the latter question when you say "bin", do you mean trash bin? I don't quite understand what "bin the outputs" means.

Hello, I am really sorry for not being specific. I should have displayed what I was trying. So here it is:

#!/usr/bin/env perl

use 5.010;

for (<>) {
    if (/^>/) {
        # Header
    } elsif (/^[A-Z]+$/) {
        # Protein
        my $a = tr/A/A/;
        say "A: $a, length: " . length;
    }
}
~
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There are two issues I am facing right now. First, some of the sequence entries in the input file are long and are continued on the next line (see below for example). But this script reads only the first line (before moving on to the second entry) due to which I'm getting wrong values for the length and number of 'A's that I want. Is there a way to fix this?

Example sequence:

>sp|P76347|YEEJ_ECOLI Uncharacterized protein YeeJ OS=Escherichia coli
+ (strain K12) OX=83333 GN=yeeJ PE=3 SV=3
MATKKRSGEEINDRQILCGMGIKLRRLTAGICLITQLAFPMAAAAQGVVNAATQQPVPAQ
IAIANANTVPYTLGALESAQSVAERFGISVAELRKLNQFRTFARGFDNVRQGDELDVPAQ
VSEKKLTPPPGNSSDNLEQQIASTSQQIGSLLAEDMNSEQAANMARGWASSQASGAMTDW
LSRFGTARITLGVDEDFSLKNSQFDFLHPWYETPDNLFFSQHTLHRTDERTQINNGLGWR
HFTPTWMSGINFFFDHDLSRYHSRAGIGAEYWRDYLKLSSNGYLRLTNWRSAPELDNDYE
ARPANGWDVRAESWLPAWPHLGGKLVYEQYYGDEVA
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Second, This script is giving me the output on the terminal. I want it to give me the output in a file. How and where do I declare the output file details?

I want it to give me the output in a file. How and where do I declare the output file details?

stevieb has already suggested that you should see open. Did you read that? Did you understand it?

What about perlintro - have you read that? If not, you really should. It even contains some very simple examples of how to open and write to files.