Messing with Perl

aoc05.pl

#!/usr/bin/perl -l
use strict;
use warnings;

# Solution to https://adventofcode.com/2020/day/5

my @seats = ();

# Collect seat IDs by parsing binary sequences
while (<>) {
	chomp;
	tr/FLBR/0011/;
	push @seats, oct("0b$_");
}
@seats = sort {$a<=>$b} @seats;

# Find highest seat ID
print $seats[$#seats];

# Find missing seat ID
my $prev = 0;
foreach (@seats) {
	last if ($prev && ($_ - $prev > 1));
	$prev = $_;
}
print $prev + 1;

aoc05.sh

#!/bin/bash

# For comparison, the equivalent solution as a shell script stitching
# together Unix primitives: `tr` to translate letters into binary
# digits; `bc` for processing arithmetic instructions to convert binary
# to decimal; `sort -g` to perform a numeric sort; `awk` to find the
# maximum (PART ONE) and to find the gap in the sequence (PART TWO).

# PART ONE
< input \
tr FLBR 0011 | cat <(echo ibase=2;) - | bc | \
	awk '$1>m{m=$1;l=$0}END{print l}'


# PART TWO
< input \
tr FLBR 0011 | cat <(echo ibase=2;) - | bc | \
	sort -g | \
	awk '{ if (prev && ($1 != prev + 1)) print $1 - 1; prev = $1 }'