FUNDAMENTALS A Complete Guide for Beginners
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.
2 Methods to Create List Using 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: Create a List Using Loops in 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: Generate List Using "for" Loop in 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, please check & execute the following Bash script:
#!/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.
After running the script, it printed the list of files containing employees in them.
Case 2: Generate List Using "while" Loop in 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.
To list numbers with a while loop, see the below bash script:
#!/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
doneThe script 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++)) increments the value of i by 1, moving to the next iteration. Finally, the echo command prints the value of every iteration until the end of the loop.
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: Create a List 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.
To list the names of months using arrays, go through the following bash script:
#!/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 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.
After running the script, it prints the list of months given inside the array.
Comparative Analysis of Methods to Generate List in Bash
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 | The list is automatically generated by loops. | Those who have little to no knowledge of programming can find it complicated to write scripts using loops. |
| Method 2 | If you generate a list using arrays, it is relatively simple, as you just have to know array syntax. | The contents of the list have to be given inside the array. |
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.
People Also Ask
What is the command to list in bash?
The ls command is used to list in Bash. This command is specifically used for making a list of directories and files.
How do you define a list in a Bash script?
A list is an associative array in Bash scripting. So, defining a list means declaring an array in Bash. The syntax to declare an array in Bash is array_name={“element1” “element2”....”elementN”}.
How do I print all list elements in Bash?
To print all elements of a Bash array, you can use the declare command with the command option -p. So, the syntax is declare -p Array_name.
How to generate UUID in shell script?
To generate UUID in a shell script, you can use the uuidgen command. This command is typically available in Unix-like systems, including Linux. For that, use the syntax, my_uuid=$(uuidgen).
How do I list all users in Bash?
To list all users in Bash, you can use the cat command along with /etc/passwd. So, this passwd file in the etc directory contains all user names and when you execute this, you can see all user names printed on your screen.
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