Brace expansion ({1..10}) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of simple brace expansion

What is the output of the following bash command?

echo {1..5}

Bash Scripting

echo {1..5}

A 1,2,3,4,5

B {1..5}

C 1 2 3 4 5 6

D 1 2 3 4 5

💡 Hint

Brace expansion generates a sequence of numbers separated by spaces.

The brace expansion {1..5} generates numbers from 1 to 5 separated by spaces when echoed.

💻 Command Output

intermediate

Brace expansion with step value

What is the output of this bash command?

echo {1..10..3}

Bash Scripting

echo {1..10..3}

A 1 4 7

B 1 4 7 10

C 1 3 6 9

D 1 2 3 4 5 6 7 8 9 10

💡 Hint

The third number in brace expansion is the step size.

The sequence starts at 1, increments by 3, and stops at or before 10: 1,4,7,10.

📝 Syntax

advanced

Identify invalid brace expansion syntax

Which of the following is NOT a valid brace expansion in bash?

A echo {5..1}

B echo {1..10..2}

C echo {1..10..0}

D echo {a..z}

💡 Hint

Step value cannot be zero in brace expansion.

A step value of zero is invalid and causes an error in bash brace expansion.

💻 Command Output

advanced

Output of nested brace expansion

What is the output of this bash command?

echo file{1..3}_{a..b}.txt

Bash Scripting

echo file{1..3}_{a..b}.txt

A file1_a.txt file1_b.txt file2_a.txt file2_b.txt file3_a.txt file3_b.txt

B file1_a.txt file2_b.txt file3_a.txt

C file{1..3}_{a..b}.txt

D file1_a.txt file1_b.txt file2_a.txt file3_b.txt

💡 Hint

Brace expansions combine all possible pairs from each set.

The command expands numbers 1 to 3 and letters a to b, combining each number with each letter.

🚀 Application

expert

Count files created by brace expansion

If you run this command:

touch log_{01..10}_{a..c}.txt

How many files will be created?

Bash Scripting

touch log_{01..10}_{a..c}.txt

A 30

B 33

C 20

D 13

💡 Hint

Multiply the count of numbers by the count of letters.

There are 10 numbers (01 to 10) and 3 letters (a to c), so 10 * 3 = 30 files.

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