advent_of_code_2020_day3_part1

  #!/bin/bash
  
  pos=1
  line_num=0
  trees=0
  while read line
  do
    len=$(echo $line | wc -c)
    char_at_pos=$(echo $line | cut -c $pos)
  
    # Calculate next pos
    pos=$(($pos + 3))
    if [ $pos -ge $len ]
    then
      pos=$((($pos % $len) + 1))
    fi
  
    # Don't count the first line
    if [ $line_num -gt 0 ]
    then
      if [ $char_at_pos != "." ]
      then
        trees=$(($trees + 1))
      fi
    fi
    line_num=$(($line_num + 1))
  done <<< $(< $1)
  
  echo $trees