What Are Single-line Comments in Bash? [2 Cases With Examples]

Single-line comments in a Bash script are the important annotation that makes the script more readable. You can use a single-line comment to add an explanation of codes or disable some particular codes for a while. So, let me turn your attention to this article which will provide a detailed interpretation of single-line comments in Bash to you.

Key Takeaways

• Learning about single-line comments in Bash.
• Getting ideas about some practical executions of single-line comments in Bash script.

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What Are Single Line Comments in Bash?

Single-line comments refer to the comments where the line starts with a hash symbol (#) and are placed before or after the code in the Bash script. These comments are kind of short and concise. Moreover, single-line comments are only for quoting a simple brief of code lines and are not executed by the interpreter or compiler.

2 Cases of Single Line Comments in Bash Scripting

Single-line comments are the less explanatory Bash comments. These are related to two points: i) Bash hashing, and ii) Inline comments. A little introduction to these two concerns is given below:

Case 1: Bash Hashing in Case of Single Line Comments

In Bash, hash (#) is the symbol for commenting out a line. A single-line comment prefixed with the hash symbol (#) adds an explanatory text without affecting the execution of codes within the Bash script. Following is an example of bash hashing in case of single-line comments with step by step procedure:

Steps to Follow >

1. Open your Ubuntu Terminal.
2. To open a script in the nano text editor, write the command below:

   nano hash-single.sh

   EXPLANATION

   • nano: A text editor.
   • hash-single.sh: This is a script that you can name by any of your choices. Here, I have named the script by ‘hash-single.sh’.
   
3. Hereafter, write the following script inside the editor:Script (hash-single.sh) >

   #!/bin/bash
   
   # This is a single-line comment
   # This is another single-line comment
   # This is one more single-line comment

   EXPLANATION

   Here, #!/bin/bash: ‘#!’ is called “Shebang” which is used for executing the bash script. The three lines ‘# This is a single-line comment’, ‘# This is another single-line comment’, and ‘# This is one more single-line comment’ dictate single-line comments as there is the hash symbol before each of these lines.

   From the above image, you can see three single-line comments which are prefixed with the hash symbol.

Case 2: Inline Comments in Case of Single Line Comments

The single-line comments that are used at the end of the coded line are specifically called inline comments. These are used at the same line of the code starting with a hash sign without moving to the next line. Below is a simple example of inline comments in case of single-line comments:

Script (single-line.sh) >

#!/bin/bash

number=20
echo "The number is: $number"  #Display the current number
number=$((number+5))  #Increment the ‘number’ variable
echo "The updated number is: $number"  #Display the updated number

You can see the single-line comments as inline comments in the above image.

3 Practical Examples of Single-line Comments in Bash

Single-line comments can be of help in various practical schemes. Now, I am going to mention some real clarifications of single-line comments in the Bash script in the following section:

Example 1: Bash Single Line Comments for Troubleshooting

For any troubleshooting purpose within Bash scripts, debugging with single-line comments is quite helpful. Below is an example of single-line comments aiding in debugging:

Script (troubleshoot.sh) >

#!/bin/bash

#Calculating the sum of numbers from 5 to a given number

#Prompt user for entering an input
read -p "Enter a positive integer:" number

#Check if the input is a positive integer
if [[ ! "$number" =~ ^[1-9][0-9]*$ ]]; then
    echo "Invalid input. Please enter a positive integer."
    exit 1
fi

#Initialize the sum variable
sum=0

#Calculate the sum using a loop
for (( i=1; i<=number; i++ )); do
    sum=$((sum + i))  #Add present value of i to the sum
    echo "Current Sum: $sum"  #Debugging: print current sum for each iteration
done

#Display the output
echo "The sum of numbers from 5 to $number is: $sum"

You can observe the step-by-step results and identify the unexpected bugs within your codes using single-line comments like the snapshot above.

Example 2: Bash Single Line Comments for Educational Purposes

You can use single-line comments for educational purposes too. These can serve as great documented resources for any kind of tutorial. Here is an easy implementation of single-line comments on finding the factorial of a given number:

Script (factorial.sh) >

#!/bin/bash

#Calculating the factorial of a given number

#Prompt user for entering an input
read -p "Enter a positive integer: " number

#Check if the input is a positive integer
if [[ ! "$number" =~ ^[1-9][0-9]*$ ]]; then
    echo "Invalid input. Please enter a positive integer."
    exit 1
fi

#Initialize the factorial variable
factorial=1

#Calculate factorial using a loop
for (( i=1; i<=number; i++ )); do
    factorial=$((factorial * i))  #Multiply factorial with current value of i
done

#Display the output
echo "The factorial of $number is: $factorial"

From the image, you can see that the single-line comments have turned the program quite easy explaining each section of the code.

Example 3: Bash Single Line Comments for Security Purposes

Single-line comments emphasize the security of a Bash script. Here’s an example of single-line comments on restricting unauthorized access to the Bash script:

Script (security.sh) >

#!/bin/bash

#IMPORTANT: Confirm that only authorized users can access the script.
#This script performs sensitive operations & must be protected.

#Check if the user is authorized
if [[ "$user" != "admin" ]]; then
    echo "Error! You cannot run this script."
    exit 1
fi

The single-line comments underlined in the above image help to define the unusual users easily.

Conclusion

To summarize, single-line comments as an essential feature serve to clarify codes or programming within a Bash script. So, count on this guide and make a practice of commenting out your code concisely.

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