Brace expansion ({1..10}) in Bash Scripting - Mini Project: Build & Apply

Using Brace Expansion to Generate Number Sequences in Bash

📖 Scenario: Imagine you are organizing a small event and need to create folders numbered from 1 to 10 to store participant files. Doing this manually would take time, so you want to automate it using a simple Bash script.

🎯 Goal: Build a Bash script that uses brace expansion {1..10} to generate a sequence of numbers and create folders named folder1 to folder10.

📋 What You'll Learn

Create a variable with the sequence of numbers from 1 to 10 using brace expansion.

Create a prefix variable for folder names.

Use a loop to combine the prefix and numbers to create folder names.

Print the folder names to verify the output.

💡 Why This Matters

🌍 Real World

Automating repetitive tasks like creating multiple folders or files saves time and reduces errors.

💼 Career

Knowing how to use brace expansion and loops in Bash is useful for system administrators, DevOps engineers, and anyone working with Linux shell scripting.

1

Create a variable with numbers 1 to 10 using brace expansion

Create a variable called numbers and assign it the sequence generated by brace expansion {1..10}.

Bash Scripting

# Create a variable called numbers with the sequence {1..10}
numbers=({1..10})

Hint

Use numbers=({1..10}) to create a sequence from 1 to 10.

2

Create a prefix variable for folder names

Add a variable called prefix and set it to the string folder.

Bash Scripting

numbers=({1..10})
prefix=folder
# Your code here

Hint

Set prefix=folder to use as the folder name start.

3

Use a loop to combine prefix and numbers to create folder names

Write a for loop using num as the iterator to go through ${numbers[@]}. Inside the loop, create a variable folder_name by combining $prefix and $num.

Bash Scripting

numbers=({1..10})
prefix=folder
for num in ${numbers[@]}; do
    folder_name="$prefix$num"
    # Your code here
 done

Hint

Use for num in ${numbers[@]} and combine with prefix inside the loop.

4

Print the folder names to verify the output

Inside the loop, add a echo statement to print the folder_name variable.

Bash Scripting

numbers=({1..10})
prefix=folder
for num in ${numbers[@]}; do
    folder_name="$prefix$num"
    # Print folder_name here
 done

Hint

Use echo "$folder_name" inside the loop to print each folder name.

Practice

1. What does the Bash brace expansion {1..5} produce when used in a command?

easy

A. A sequence of numbers: 1 2 3 4 5

B. A sequence of letters: a b c d e

C. A syntax error

D. A single string: {1..5}

Solution

1. Step 1: Understand brace expansion syntax

   The syntax {start..end} generates a sequence of numbers or letters from start to end.

2. Step 2: Apply to numbers 1 to 5

   Using {1..5} produces the numbers 1, 2, 3, 4, 5 separated by spaces.

3. Final Answer:

   A sequence of numbers: 1 2 3 4 5 -> Option A

4. Quick Check:

   Brace expansion {1..5} = 1 2 3 4 5 [OK]

Hint: Brace expansion {x..y} lists numbers or letters from x to y [OK]

Common Mistakes:

• Thinking it outputs letters for numbers
• Expecting a syntax error
• Assuming it outputs the literal string

2. Which of the following is the correct syntax to generate numbers from 3 to 7 using brace expansion in Bash?

easy

A. echo [3..7]

B. echo {3-7}

C. echo (3..7)

D. echo {3..7}

Solution

1. Step 1: Recall correct brace expansion syntax

   Brace expansion uses curly braces with two dots: {start..end}.

2. Step 2: Check each option

   Only echo {3..7} uses correct braces and dots. Others use wrong symbols like parentheses, brackets, or hyphens.

3. Final Answer:

   echo {3..7} -> Option D

4. Quick Check:

   Correct syntax uses curly braces and two dots [OK]

Hint: Use curly braces and two dots for sequences {start..end} [OK]

Common Mistakes:

• Using parentheses or brackets instead of braces
• Using a hyphen instead of two dots
• Missing braces entirely

3. What is the output of the following Bash command?

echo file{1..3}.txt

medium

A. file1.txt file2.txt file3.txt

B. file{1..3}.txt

C. file1 file2 file3.txt

D. file1.txt file2.txt file3

Solution

1. Step 1: Understand brace expansion with suffix

   The brace expansion {1..3} generates 1 2 3, and the suffix .txt is added to each.

2. Step 2: Combine parts

   Each expanded number is combined with 'file' prefix and '.txt' suffix, producing: file1.txt file2.txt file3.txt.

3. Final Answer:

   file1.txt file2.txt file3.txt -> Option A

4. Quick Check:

   Brace expansion with suffix repeats suffix for each number [OK]

Hint: Brace expansion repeats suffix/prefix for each number [OK]

Common Mistakes:

• Expecting literal braces in output
• Missing suffix on some items
• Mixing suffix placement

4. Identify the error in this Bash command:

echo {1..5..2}

medium

A. Outputs 1 2 3 4 5

B. Syntax error: too many dots

C. No error; outputs 1 3 5

D. Outputs nothing

Solution

1. Step 1: Understand brace expansion with step

   The syntax {start..end..step} is valid in Bash to generate sequences with a step.

2. Step 2: Apply to {1..5..2}

   This generates numbers starting at 1, stepping by 2, up to 5: 1, 3, 5.

3. Final Answer:

   No error; outputs 1 3 5 -> Option C

4. Quick Check:

   Brace expansion supports step with two dots between numbers [OK]

Hint: Brace expansion can include step: {start..end..step} [OK]

Common Mistakes:

• Thinking extra dots cause syntax error
• Expecting continuous sequence ignoring step
• Assuming no output for step usage

5. You want to create empty files named log1.txt through log10.txt using a single Bash command with brace expansion. Which command achieves this?

hard

A. touch log{1..10}

B. touch log{1..10}.txt

C. touch log{1..10}.txt.txt

D. touch log{1..10.txt}

Solution

1. Step 1: Understand the goal

   You want files named log1.txt, log2.txt, ..., log10.txt created.

2. Step 2: Use brace expansion with suffix

   The correct syntax is touch log{1..10}.txt, which expands to log1.txt, log2.txt, ..., log10.txt.

3. Step 3: Check other options

   touch log{1..10} omits the .txt suffix; touch log{1..10.txt} has invalid syntax with .txt inside braces; touch log{1..10}.txt.txt adds an extra .txt to each filename.

4. Final Answer:

   touch log{1..10}.txt -> Option B

5. Quick Check:

   Brace expansion with suffix creates all files at once [OK]

Hint: Use touch with brace expansion and suffix: touch name{1..n}.ext [OK]

Common Mistakes:

• Placing suffix inside braces incorrectly
• Adding extra suffixes
• Omitting suffix leading to wrong filenames