Working with Array in Shell Scripting
First, let's understand how to create an array using Shell Scripting.
Syntax:
arrayName[subscript] = value
Example:
declare -a myArray
myArray[0]=value
OR
declare -A myArray
myArray[key]=value
Notice a lowercase "a" in the first line used to declare an indexed array. Also, there is a capital "A" in the next example. This is used to declare an associative array.
Accessing Array Elements
As we know, we can access the array elements that are being indexed individually. We can access all the elements by specifying the array index as shown below:
myArray[element]="Hey Ninjas"
echo ${myArray[element]}
Output
Hey Ninjas
The above given is an example of Associate Arrays. Let's now check out the indexed array example.
myArray=(1 2 3 4 5)
echo ${myArray[2]}
Output
3
Reading Array Elements
We will use the loop concept here. It will be very easy if you are already familiar with the loop concepts.
myArray=(1 2 3 4 5 6 7 8)
for i in ${myArray[@]}
do
echo $i
done
Output
1
2
3
4
5
6
7
8
Here, You must have thought about what myArray[@] is. So, the [@] symbol is used to print all the elements at the same time.
Note that we can perform the same using the [*] symbol.
Now, we will check how to print elements from a specific index. Let's see the syntax first.
echo ${arrrayName[whichElement]:startingIndex}
We are now moving toward an example of the same.
myArray=(I really love Coding Ninjas)
echo ${myArray[@]:0}
echo ${myArray[@]:1}
echo ${myArray[@]:2}
echo ${myArray[0]:1}
Output:
The last line echo ${myArray[0]:1} will not print anything as the 0th element (I) does not have enough characters to print.
We can also print the element within any given range. Let's understand this using an example.
The syntax says:
echo ${arrayName[whichElement]:startingIndex:countElement}
Example:
myArray=(I really love Coding Ninjas)
echo ${myArray[@]:1:4}
echo ${myArray[@]:2:3}
echo ${myArray[@]:3:4}
echo ${myArray[0]:1:3}
Output:
The reason for not printing the output for the echo ${myArray[0]:1:3} line is the same. The 0th element (I) does not have enough characters to print.
Counting the Number of Elements
There is a symbol similar to @, #. This # symbol is used to get the count of the elements in the given array. Let's test this using an example.
myArray=(1 2 3 4 5)
echo ${#myArray[@]}
Output:
5
Delete a Single Array Element
The "unset" keyword is used to delete any specific element in an array. We just have to give the array name and the index of the element that we wish to remove. Let's check this out using an example.
myArray=(1 2 3 4 5 6 7 8)
printf "Array before delete:\n"
for i in ${myArray[@]}
do
echo $i
done
unset myArray[2]
printf "Array after delete:\n"
for i in ${myArray[@]}
do
echo $i
done
Output:
Array before delete:
1
2
3
4
5
6
7
8
Array after delete:
1
2
4
5
6
7
8
Search and Replace Array Element
Now we will learn how to search and replace an array element or any character in an array. Let's take an example for better understanding.
Syntax:
echo ${arrayName[@]//character/replacement}
Example:
myArr=(My fav learning website is Coding Ninjas)
echo ${myArr[@]//fav/favourite} #changing a complete element
echo ${myArr[@]//d/D} #changing a character in an element
Output:
Check out this problem - Maximum Product Subarray
Frequently Asked Questions
What is the N in a shell script?
You can use the \n character instead of repeatedly echoing to start new lines in your shell script. For Unix-based systems, the \n is a newline character that helps move the commands that follow it to a new line.
Is string empty bash?
To check if a string is empty in Bash, we can make an equality check with a given string and empty the string using the string equal-to = operator. The other way is to use the -z string operator to check if the size of the given string operand is zero.
What is the Bash test?
A test in bash is not a test of the function of your app. It is a way of showing a statement that may or may not be true. You can use tests in bash to put conditional commands into practice. They contain what is being tested in square brackets, i.e., [and].
Conclusion
This article discusses the topic of Array variables in Shell Scripting. In detail, we have seen the Array variables in Shell Scripting, working with an array in the shell script, including accessing, reading, counting, and deleting using array elements.
We hope this blog has helped you enhance your knowledge of Array variables in Shell Scripting. If you want to learn more, then check out our articles.
Shell Scripting - Arithmetic Operations.
Shell Scripting Interview Question.
Linux - Shell Variables.
Array in Javascript
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