Working with Arrays in Linux Shell, bash and zsh, examples for https://blog.mimacom.com/arrays-on-linux-shell/

array-demo-improved.sh

#!/usr/bin/zsh

echo "detecting shell:"
if [[ -n ${ZSH_VERSION} ]] && [[ ! -z ${ZSH_VERSION} ]]; then
  INDEX_START=1
  INDEX_OFFSET=0
  echo "  using zsh $ZSH_VERSION, index starts at $INDEX_START"
elif [[ -n $BASH_VERSION ]]; then
  INDEX_START=0
  INDEX_OFFSET=1
  echo "  using bash $BASH_VERSION, index starts at $INDEX_START"
else
  echo "  unknown"
fi
echo

# example data
my_array=(
"¯\_(ツ)_/¯"
"This"
"is"
"a"
"string"
"array"
"ᕙ(⇀‸↼‶)ᕗ"
)

# ${my_array[@]} - all of the items in the array
echo "array: ${my_array[@]}"
echo

# access item with index position
echo "index 5: ${my_array[5 - $INDEX_OFFSET]}"
echo

# ${#my_array[@]} - number of items in the array
echo "length: ${#my_array[@]}"
echo

# last element
if [[ -n $ZSH_VERSION ]]; then
  echo "last index: ${my_array[-1]}"
elif [[ -n $BASH_VERSION ]]; then
  # access last item, usually -1 works, on bash > v4.3
  # mac os shell is v3,2
  length=${#my_array[@]}
  echo "last index: ${my_array[$length-$INDEX_OFFSET]}"
fi
echo

# ${#my_array[$INDEX_START]} - length of first item in array
echo "item: ${my_array[$INDEX_START]} has a length of ${#my_array[$INDEX_START]}"
echo

# ${my_array[@]} - iterate over values
echo "iterate over array"
for i in "${my_array[@]}"; do
  echo "  $i"
done
echo


echo "iterate with index"
if [[ -z $ZSH_VERSION ]]; then
  # ${!my_array[@]} - all of the indexes in the array
  for i in "${!my_array[@]}"; do
    echo "index: ${i}, value: ${my_array[$i]}"
  done
else
  length=${#my_array[@]}
  for i in $(seq 1 ${length}); do
    echo "index: ${i}, value: ${my_array[$i]}"
  done
fi
echo

array-demo.sh

#!/usr/bin/env bash

echo "detecting shell:"
if [[ -n ${ZSH_VERSION} ]] && [[ ! -z ${ZSH_VERSION} ]]; then
  echo "  using zsh $ZSH_VERSION"
elif [[ -n $BASH_VERSION ]]; then
  echo "  using bash $BASH_VERSION"
else
  echo "  unknown"
fi
echo

# example data
my_array=(
"¯\_(ツ)_/¯"
"This"
"is"
"a"
"string"
"array"
"ᕙ(⇀‸↼‶)ᕗ"
)

# ${my_array[@]} - all of the items in the array
echo "array: ${my_array[@]}"
echo

# access item with index position
echo "index 5: ${my_array[5]}"
echo

# ${#my_array[@]} - number of items in the array
echo "length: ${#my_array[@]}"
echo

# access last item, usually -1 works, on bash > v4.3
# mac os shell is v3,2
length=${#my_array[@]}
echo "last index: ${my_array[$length-1]}"
echo

# ${#my_array[0]} - length of item zero
echo "item: ${my_array[0]} has a length of ${#my_array[0]}"
echo

# ${my_array[@]} - iterate over values
echo "iterate over array"
for i in "${my_array[@]}"; do
  echo "  $i"
done
echo

# don't run this if zsh is running, version not set
if [[ -z $ZSH_VERSION ]]; then
  # ${!my_array[@]} - all of the indexes in the array
  echo "iterate with index"
  for i in "${!my_array[@]}"; do
    echo "index: ${i}, value: ${my_array[$i]}"
  done
  echo
fi