Could you elaborate a little? I ask because the Perl 5 code looks a lot like the Perl that I write. I'd like to improve, but the existing Perl code that I'm writing on top of is really bad. Like really, really bad. I don't have much quality Perl to compare against.

Two examples:

    $freq{substr $grade{$_}, 0, 1}++ for keys %grade;

better:

    $freq{$_}++ for map { substr $_, 0, 1 } values %grade;

best:

    my @letters = map { substr $_, 0, 1 } values %grade;
    $freq{$_}++ for @letters;

----------------------------

and

    open my $fh, '<:utf8', "grades.txt"
        or die "Failed to open file: $!";
    
    my %grade;
    while (<$fh>) {
        m/^(\w+) \s+ ([A-F][+-]?)$/x
        or die "Can't parse line '$_'";
        $grade{$1} = $2;
    };

better:

    use 5.010;
    use IO::All -binary, -utf8;
    
    my $line_format = qr/
        ^               	    # line start
        (?<student>\w+)         # name
        \s+                     # gap
        (?<grade>[A-F][+-]?)    # grade
        $                       # line end
    /x;
    
    my $fh = io->file("grades.txt");
    my %grade;
    while (my $line = $io->getline) {
        die "Can't parse line '$line'" if $line !~ $line_format;
        $grade{$+{student}} = $+{grade};
    }

Very nicely done. I use Perl in my everyday job, and its nice to see that some people still know how to write good Perl.

You should have use strict; use warnings; then you would have noticed the my $fh and the $io->getline error

Dammit, you're right. I was working in a buffer without perl instrumentation enabled because i was composing a comment, not a script. Now i can't edit the comment anymore. :/

5.10 in production? Surely you're joking! 5.8 or bust.

Exactly. Perl's critics often completely overlook the degree to which liberal use of the map/reduce paradigm can simplify the graphical representation of your code and allow the powerful list processing features to be brought to bear. Consider:

    use strict; use warnings; use List::Util

    qw/reduce/;
    map { print } join "\n", "Distribution of grades by letter:",
    map { sprintf(  "\t%s: %s student%s",   @$_,   $_ -> [1] == 1 ? '' : 's'  )    }
    map { my   $c   =   $_   ;    sort   {   $a  ->  [0]   cmp    $b   ->   [0]    }
    map { [ $_, $c->{$_} ] } keys %$c } reduce { $a->{chr(ord($b->[1]))}++; $a } {},
    map { printf(  "List of students with failing grades:\n\t%s\n",   join  ', '   ,
    map { $_->[0] } grep {ord $_->[1] >68} @$_); @$_} reduce {push(@$a, $b); $a} [],
    map { printf( "${^A}'s grade: %s\n"  ,  $_ -> [1] )  if  $_->[0]  eq  $^A;  $_ }
    map { $^A="Zsófia"; [split(/\s+/)] } <STDIN>       

The use of strict and warnings making this particularly Modern Perl, you could almost be forgiven for thinking you were reading Haskell...

needs use feature 'say'