Bash Arrays

Array Declaration syntax

Indexes and Metadata

Destroying Arrays

The unset builtin command is used to destroy (unset) arrays or individual elements of arrays.

Storing Values

Getting values

<aside> 🔗 For clarification: When you use the subscripts @ or * for mass-expanding, then the behaviour is exactly what it is for $@ and $*  when mass-expanding the positional parameters. You should read this article to understand what's going on.

</aside>

<aside> 💡 It is best to explicitly specify -v when unsetting variables with unset.

</aside>

<aside> 💡 Learn more about bash Arrays here

</aside>

Array Discussion

Compound indexed array assignment

# 
:'
Compound array assignment - sets the whole array
NAMES to the given list of elements.
'
# NAMES => Creg Jan Anna
NAMES=('Creg' 'Jan' 'Anna')

# using the declare construct
declare -a Numbers=(1 2 3)

Indexed array assignment using brace expansion

ARRAY1=(foo{1..2}) # => foo1 foo2

ARRAY2=({A..D})    # => A B C D

ARRAY3=({1..5})    # => 1 2 3 4 5

ARRAY4=({A..B}{1..2}) #=> A1 A2 B1 B2

Index array assignment

:'
Sets the element N of the indexed array NAMES to
VALUE. 
N can be any valid arithmetic expression.
'

NAMES[0]='Creg'
NAMES[1]='Jan'
NAMES[2]='Anna'
# NAMES => Creg Jan Anna

Appending values to arrays

NAMES=('Creg' 'Jan' 'Anna')

NAMES+=('Jay' 'Jimmy' 'Tom')
# NAMES => Creg Jan Anna Jay Jimmy Tom

# This is also the same as
NAMES=(${NAMES[@]} 'Jay' 'Jimmy' 'Tom')
# NAMES => Creg Jan Anna Jay Jimmy Tom

Compound associative array assignment

:'
Individual mass-setting for **associative arrays**. 
The named indexes (here: name, age....) are strings.
'

declare -A person # this line is required
# quotes can me omitted for the keys, see the **age** key below
person=(["name"]="Jay" [age]=22 ["eye_color"]="blue")

# person => Jay 22 blue

Merging/Concatenating Arrays

ARRAY1=(foo{1..2}) # => foo1 foo2
ARRAY2=({A..D})    # => A B C D
ARRAY3=({1..5})    # => 1 2 3 4 5

# Merge Arrays => foo1 foo2 A B C D 1 2 3 4 5
ARRAY4=(${ARRAY1[@]} ${ARRAY2[@]} ${ARRAY3[@]})

The **@** can also be replace with a *****

Key associative array assignment

declare -A person

person[name]="Jay"

person[age]=22

person[eye_color]="blue"

# person => Jay 22 blue

Iterating an indexed array

names=('Jay' 'Joe' 'Jimmy')
for name in "${names[@]}"; do
    echo $name
done

# using index
for i in "${!names[@]}"; do
  printf "%s\\t%s\\n" "$i" "${names[$i]}"
done

Working with associative arrays

declare -A person 
person=(["name"]="Jay" [age]=22 ["eye_color"]="blue")

echo ${person[name]} #  Get person's name
echo ${sounds[@]}   # Get all person's values
echo ${sounds[*]}  # Get all person's values
echo ${!person[@]}  # All person's  keys (age, name...)
echo ${#person[@]}  # Number of elements

unset -v person[age]   # Delete person's age

# All of the above operations workes with index arrays, just that you only 
# replace the keys with indexes

Iterating an associative array

declare -A person 
person=(["name"]="Jay" [age]=22 ["eye_color"]="blue")

for value in "${person[@]}"; do
    echo $value
done

# Using keys
for key in "${!person[@]}"; do
    echo "$key  ${person[$key]}"
done

Array arguments

function extract()
{
    # creating a local array from function argument 1 ($1)
    local -n local_names=$1
	  # creating a local index from function argument 2 ($2)
    local index=$2
    echo "${local_names[$index]}"
 }
# defining global array names
names=('Jay' 'Joe' 'Jimmy')

extract names 2     # => Jimmy