#!/usr/bin/perl
use v5.35.0;

# Slurp the whole map as a single string, regularize its
# line terminators, work out how big it is, and set up deltas
# for moving one step in each of the four available directions

local $/ = undef;
local $_ = <>;
s/\v+/\n/g;
my $row = 1 + index $_, "\n";
my $len = length;
my @dp = (1, -$row, -1, $row);

# Find the guard's starting position and direction

/([>^<v])/g;
my $pos = (pos) - 1;
(my $dir = $1) =~ tr/>^<v/0123/;

# Walk the guard's route

for (;;) {
	substr($_, $pos, 1) = 'X';	# Mark route
	$pos += $dp[$dir];		# Advance

	# Done if edge hit
	last unless 0 <= $pos < $len;
	my $cell = substr($_, $pos, 1);
	last if $cell eq "\n";
	
	if ($cell eq "#") {		# Obstacle?
		$pos -= $dp[$dir];	# Retreat
		$dir = ($dir - 1) & 3;	# Turn right
	}
}

say s/X//g;