Bash array - how to use arrays in Unix shell

Unix shell do support array. Yes, it does. Please refer to https://opensource.com/article/18/5/you-dont-know-bash-intro-bash-arrays OR https://www.tutorialspoint.com/unix/unix-using-arrays.htm for more info on this. To define an array, do;

myArray=(the quick brown fox jumps over the lazy dog)

But how to read an array?. Lets try this;

#!/bin/bash
myArray=(the quick brown fox jumps over the lazy dog)
echo $myArray

Run it ...

# ./test.sh
the

It will only echo the 1st word from the array. Lets try another example.

#!/bin/bash
myArray=(the quick brown fox jumps over the lazy dog)
echo ${myArray[0]}
echo ${myArray[1]}
echo ${myArray[2]}
echo ${myArray[3]}
echo ${myArray[4]}
echo ${myArray[5]}
echo ${myArray[6]}
echo ${myArray[7]}
echo ${myArray[8]}
echo ${myArray[9]}

Run it ...

# ./test.sh
the
quick
brown
fox
jumps
over
the
lazy
dog

Now, It will print all array content. Note that, it won't give any alert if the index is out of bound, for this example = "${myArray[9]}" Lets do a proper way to read an array by using "for loop";

#!/bin/bash
myArray=(the quick brown fox jumps over the lazy dog)
for i in ${myArray[@]}
do
    echo $i
done

Run it ...

# ./test.sh
the
quick
brown
fox
jumps
over
the
lazy
dog

You will get above output. Adding an "!" to the array name will change the loop from looping through the values to looping through the indices.

#!/bin/bash
myArray=(the quick brown fox jumps over the lazy dog)
for i in ${!myArray[@]}
do
    echo $i
done

Run it ...

# ./test.sh
0
1
2
3
4
5
6
7
8

Example below is using "while loop" to loop through the array.

#!/bin/bash
myArray=(the quick brown fox jumps over the lazy dog)
index=0
while [ $index -lt ${#myArray[@]} ]
do
    echo $index = ${myArray[index]}
    index=`expr $index + 1`
done

Run it ...

# ./test.sh
0 = the
1 = quick
2 = brown
3 = fox
4 = jumps
5 = over
6 = the
7 = lazy
8 = dog

Here are some syntax list that might be useful.

Syntax	Result
myArray=()	Create an empty array
myArray=(1 2 3)	Initialize array
${myArray[2]}	Retrieve all elements
${myArray[@]}	Retrieve all elements
${!myArray[@]}	Retrieve array indices
${#myArray[@]}	Calculate array size
myArray[0]=3	Overwrite 1st element
myArray+=(4)	Append value(s)
${arr[@]:s:n}	Retrieve n elements starting at index s