@cassidoo's interview question from December 12, 2021

makeTree.sh

#!/usr/bin/env bash
set -eu -o pipefail

# Given a file named merry-christmas.txt that has a single integer x in it, write a script
# to generate a Christmas tree with asterisks (*) and output it as happy-holidays.txt. The
# tree should have a height of x, and if merry-christmas.txt is empty, the height should
# be 25 asterisks tall. 

IN_FILE="merry-christmas.txt"
OUT_FILE="happy-holidays.txt"

if ! [ -f ${IN_FILE} ]; then
  echo "Can't find ${IN_FILE}"
  exit 1
fi
if [ -f ${OUT_FILE} ]; then
  read -p "${OUT_FILE} exists, overwrite? " -n 1 -r
  echo
  if [[ ! $REPLY =~ ^[Yy]$ ]]; then
    exit 1
  fi
  :>${OUT_FILE}
fi

read -r lines < ${IN_FILE} || :
if [ -v $lines ] || ! [[ $lines =~ ^[0-9]+$ ]]; then
  lines=25
fi

for ((row=1; row<=$lines; row++)); do
  num_spaces=$((lines-row))
  num_stars=$(((2 * row) -1))
  printf -v row_spaces '%*s' $num_spaces
  printf -v row_stars '*%.0s' $(seq 1 $num_stars)
  echo "${row_spaces}${row_stars}" >> ${OUT_FILE}
done

if [ $# -gt 0 ]; then
  if [ "$1" == "base" ]; then
    num_spaces=$((lines-1))
    printf -v pole_spaces '%*s' $num_spaces
    echo "${pole_spaces}|" >> ${OUT_FILE}
    base_length=$((lines / 2))
    if [ $(( base_length % 2)) ]; then ((base_length++)); fi
    num_spaces=$(((num_stars - base_length) / 2 ))
    printf -v base_spaces '%*s' $num_spaces
    printf -v base '=%.0s' $(seq 1 $base_length)
    echo "${base_spaces}${base}" >> ${OUT_FILE}
  fi
fi

echo
cat ${OUT_FILE}

MONTASIO:scripts andrewrich$ echo 3 > merry-christmas.txt 
MONTASIO:scripts andrewrich$ ./makeTree.sh

  *
 ***
*****
MONTASIO:scripts andrewrich$ :>merry-christmas.txt 
MONTASIO:scripts andrewrich$ ./makeTree.sh
happy-holidays.txt exists, overwrite? y

                        *
                       ***
                      *****
                     *******
                    *********
                   ***********
                  *************
                 ***************
                *****************
               *******************
              *********************
             ***********************
            *************************
           ***************************
          *****************************
         *******************************
        *********************************
       ***********************************
      *************************************
     ***************************************
    *****************************************
   *******************************************
  *********************************************
 ***********************************************
*************************************************
MONTASIO:scripts andrewrich$ ./makeTree.sh base
happy-holidays.txt exists, overwrite? y

                        *
                       ***
                      *****
                     *******
                    *********
                   ***********
                  *************
                 ***************
                *****************
               *******************
              *********************
             ***********************
            *************************
           ***************************
          *****************************
         *******************************
        *********************************
       ***********************************
      *************************************
     ***************************************
    *****************************************
   *******************************************
  *********************************************
 ***********************************************
*************************************************
                        |
                  =============
MONTASIO:scripts andrewrich$ echo 4 > merry-christmas.txt 
MONTASIO:scripts andrewrich$ ./makeTree.sh base
happy-holidays.txt exists, overwrite? y

   *
  ***
 *****
*******
   |
  ===