2.12. Blocks

Never place two statements on the same line.

If two or more statements share one line, each of them becomes harder to comprehend:

    RECORD:
    while (my $record = <$inventory_file>) {
        chomp $record; next RECORD if $record eq $EMPTY_STR;
        my @fields = split $FIELD_SEPARATOR, $record; update_sales(\@fields);$count++;
    }

You're already saving vertical space by using K&R bracketing; use that space to improve the code's readability, by giving each statement its own line:

    RECORD:
    while (my $record = <$inventory_file>) {
        chomp $record;
        next RECORD if $record eq $EMPTY_STR;
        my @fields = split $FIELD_SEPARATOR, $record;
        update_sales(\@fields);
        $count++;
    }

Note that this guideline applies even to map and grep blocks that contain more than one statement. You should write:

    my @clean_words
        = map {
              my $word = $_;
              $word =~ s/$EXPLETIVE/[DELETED]/gxms;
              $word;
          } @raw_words;

not:

    my @clean_words
        = map { my $word = $_; $word =~ s/$EXPLETIVE/[DELETED]/gxms; $word } @raw_words;