In Bash, there is no data type named “list”, but you can generate a list using bash scripts that you can use for your needs. Also, sometimes associative arrays are referred to as lists in Bash scripting. In this article, I will demonstrate how to create a list in Bash scripts and give some examples.
Key Takeaways
- Learning to generate a list using Bash script.
- Learning to use loops and arrays to generate a list and know which to use when.
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2 Methods to List in Bash Scripts
In this article, you are going to learn how to use loops and arrays to generate lists using Bash script. You can use either of the methods to create a list. Also, you will notice that while using an array, I have written all the contents of the list inside the array. On the other hand, when I used loops, the list was generated by the loop.
Method 1: Generate a List with Loops Using Bash Scripts
In this method, you will see how to generate a list using for and while loops. Also, I have tried to make this list generation interactive, so that users can use it according to their needs.
Case 1: List Files with for Loop Using Bash Script
Suppose, I want to list files with “employee” in the name. To do so I’ve used for loop to go through the files in loops. If you want to achieve this, follow the below steps.
➊ First, launch the Ubuntu terminal. However, you can use the shortcut keys CTRL+ALT+T to do so.
➋ Then create a file with the extension .sh using the nano command and open the script in the text editor like the following.
nano list_files.sh- nano: Opens and creates a file in the nano text editor.
- list_files.sh: File name.
➌ After that, copy the following script into your text editor.
#!/bin/bash
#listing all files named employee
for a in $(ls employee*)
do
ls -l "$a"
doneThe first line, #!/bin/bash is called shebang, which specifies the interpreter as Bash, which will be used to execute the script. Then, the for loop iterates over the list of files in the current directory that contain the name “employee” and the output is captured and processed by the loop. After that, the line ls -l “$a” basically executes the ls -l command for each file captured by the loop and displays detailed information about the file, including its permission, owner, size, and modification timestamp. Finally, the “$a” is to represent the current file being processed in each iteration.
➎ Now, you need to make the bash script file executable. Type the following line in the terminal to do so.
chmod +x list_files.sh- chmod: Changes the permissions of files and directories.
- +x: Argument with the chmod command to add the executable permission.
- list_files.sh: File that you want to make executable.
➏ Finally, you can simply run the file from your command line by executing:
./list_files.sh
After running the script, it printed the list of files containing employees in them.
Case 2: List Numbers with while Loop Using Bash Script
In this case, I will show you how to generate a list of numbers using a while loop. Also, to make this script more interactive, the list of numbers will take user input. So, you can get the list of numbers according to your choice.
Script (list_numbers.sh) >
#!/bin/bash
#Prompt user to enter the number of iterations
read -p "Enter the number of iterations: " total_iterations
i=1 #current iteration
# Start the loop
while [ $i -le $total_iterations ]
do
echo "$i" # Print the current iteration
((i++)) # Increment the counter variable
doneAs in the first script, this code starts with #!/bin/bash, which specifies the Bash interpreter. The next line prompts the user to enter the number of iterations and store it in the variable named total_iterations. Then i=1 is used to declare and initialize the variable i to 1 which represents the current iteration. After that, a while loop continues until the value i is less than or equal to the total_iterations. The ((i++)) actually increments the value of i by 1, moving to the next iteration. Finally, the echo command prints the value of each and every iteration until the end of the loop.
Use this command to run the script:
./list_numbers.sh
After running the script, a user prompt takes the iteration number from the user. According to the inserted number, the script prints numbers. For example, as I entered 7, it showed a list of numbers from 1 to 7.
Method 2: List Name of Months Using Arrays in Bash Scripts
In this method, I have demonstrated the process of generating any list using an array. I have generated a list of months. Moreover, you can use the array to generate any list you want, you just have to change the list’s contents.
Script (list_months.sh) >
#!/bin/bash
# Declare an array of month names
Months=("January" "February" "March" "April" "May" "June" "July" "August" "September" "October" "November" "December")
# Print the list of months
echo "The list of Months: ${Months[@]}"This script starts with #!/bin/bash, which specifies the Bash interpreter. The next line declares an array named Months, which contains the names of months. Finally, the echo command prints the list of months, and ${Months[@]} expands the array to include all elements.
Use this command to run the script:
./list_months.sh
After running the script, it prints the list of months given inside the array.
Comparative Analysis of the Methods
In this section, I will give you a comparative analysis of the two methods mentioned above so you can understand which will be best for you to use.
| Methods | Pros | Cons |
|---|---|---|
| Method 1 |
|
|
| Method 2 |
|
|
If you want to generate a list automatically, you better use the first method, but you must have a firm understanding of conditional loops. On the other hand, if you already have a list and want to manipulate it and print it in different ways, you should go for the second method.
Conclusion
So far, you’ve learned to generate a list with Bash scripting. Using loops or arrays, you can now quickly create lists. Choose the one that best suits your needs. Feel free to ask any questions regarding this article.
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