for loop with range ({1..10}) in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the syntax for i in {1..10} do in a bash script?

It creates a loop that runs 10 times, with the variable i taking values from 1 to 10 in order.

beginner

How do you print numbers 1 to 10 using a for loop with range in bash?

Use:
for i in {1..10}; do
echo $i
done
This prints numbers 1 through 10, each on its own line.

intermediate

Can the range in {1..10} be changed to count backwards?

Yes. You can write {10..1} to count down from 10 to 1 in the loop.

intermediate

What happens if you use for i in {1..10..2} in bash?

The loop counts from 1 to 10 in steps of 2, so i takes values 1, 3, 5, 7, 9.

advanced

Why is for i in {1..10} preferred over using seq 1 10 in some cases?

Because {1..10} is a bash brace expansion that is faster and does not require calling an external command like seq.

What will the following bash code print?
for i in {1..5}; do echo $((i * 2)); done

A 5 10 15 20 25

B 1 2 3 4 5

C 2 4 6 8 10

D Error

The loop runs from 1 to 5. Each number is multiplied by 2 and printed.

How do you write a for loop in bash to count down from 5 to 1?

A for i in {1..5}; do ... done

B for i in {5..1}; do ... done

C for i in seq 5 1; do ... done

D for i in (5..1); do ... done

Brace expansion {5..1} counts down from 5 to 1.

What does the '..' operator do in {1..10} in bash?

A It creates a list of numbers from 1 to 10

B It performs a subtraction

C It is a syntax error

D It creates a string '1..10'

Brace expansion with '..' generates a sequence of numbers.

Which of these is a valid way to loop over numbers 1 to 10 in bash?

A for i in (1..10); do echo $i; done

B for i in <1..10>; do echo $i; done

C for i in [1..10]; do echo $i; done

D for i in {1..10}; do echo $i; done

Only brace expansion {1..10} is valid syntax for this.

What will for i in {1..10..3} do?

A Loop from 1 to 10 in steps of 3

B Loop from 1 to 3 ten times

C Loop from 3 to 10 in steps of 1

D Syntax error

The third number is the step size in brace expansion.

Explain how to use a for loop with a range in bash to print numbers 1 to 10.

Think about how to write a loop that repeats 10 times with numbers from 1 to 10.

Describe how to modify the range in a bash for loop to count backwards or use steps.

Consider how the numbers inside braces control the loop sequence.

Practice

1. What does the following Bash loop do?
for i in {1..5}; do echo $i; done

easy

A. Causes a syntax error

B. Prints numbers 1 to 5, each on a new line

C. Prints numbers 0 to 4, each on a new line

D. Prints the string '{1..5}' once

Solution

1. Step 1: Understand the loop range syntax

   The loop uses {1..5}, which expands to numbers 1, 2, 3, 4, 5.

2. Step 2: Check the loop body output

   Each iteration prints the current number, so numbers 1 to 5 print on separate lines.

3. Final Answer:

   Prints numbers 1 to 5, each on a new line -> Option B

4. Quick Check:

   Range {1..5} loops from 1 to 5 [OK]

Hint: Curly braces {1..5} generate numbers 1 to 5 [OK]

Common Mistakes:

• Thinking {1..5} is a string, not a range
• Confusing range start and end values
• Expecting zero-based counting

2. Which of the following is the correct syntax to loop from 1 to 10 in Bash using brace expansion?

easy

A. for i in {1..10}; do echo $i; done

B. for i in [1..10]; do echo $i; done

C. for i in (1..10); do echo $i; done

D. for i in <1..10>; do echo $i; done

Solution

1. Step 1: Identify correct brace expansion syntax

   Bash uses curly braces {start..end} for ranges, so {1..10} is correct.

2. Step 2: Check other options for syntax errors

   Parentheses, square brackets, and angle brackets are invalid for this purpose in Bash loops.

3. Final Answer:

   for i in {1..10}; do echo $i; done -> Option A

4. Quick Check:

   Brace expansion uses curly braces {..} [OK]

Hint: Use curly braces {start..end} for ranges in Bash loops [OK]

Common Mistakes:

• Using parentheses or brackets instead of braces
• Missing the 'in' keyword
• Forgetting to close the loop with 'done'

3. What is the output of this script?

for i in {3..6}; do echo $((i * 2)); done

medium

A. 2 4 6 8

B. 3 4 5 6

C. 6
8
10
12

D. Error: invalid arithmetic

Solution

1. Step 1: Identify loop values

   The loop variable i takes values 3, 4, 5, 6 from {3..6}.

2. Step 2: Calculate output for each iteration

   Each iteration prints i * 2: 3*2=6, 4*2=8, 5*2=10, 6*2=12.

3. Final Answer:

   6 8 10 12 -> Option C

4. Quick Check:

   Multiply each i by 2 [OK]

Hint: Multiply loop variable inside $(( )) for arithmetic [OK]

Common Mistakes:

• Confusing loop values with output
• Using single parentheses instead of $(( ))
• Expecting space-separated output on one line

4. Find the error in this Bash loop:

for i in {1..5} do
echo $i
done

medium

A. Variable $i is not defined

B. Loop body must be on the same line as for

C. Brace expansion syntax is wrong

D. Missing semicolon or newline after {1..5}

Solution

1. Step 1: Check for syntax correctness in loop header

   The for loop header must end with a semicolon or newline before 'do'. Here, 'do' follows directly after {1..5} without either, causing a syntax error.

2. Step 2: Verify other parts

   Variable $i is defined by the loop, brace syntax is correct, and loop body can be on next lines.

3. Final Answer:

   Missing semicolon or newline after {1..5} -> Option D

4. Quick Check:

   Loop header must end properly before 'do' [OK]

Hint: Put semicolon or newline before 'do' in for loops [OK]

Common Mistakes:

• Omitting semicolon or newline before 'do'
• Misunderstanding brace expansion syntax
• Thinking loop body must be on same line

5. You want to print only even numbers from 2 to 10 using a Bash for loop with brace expansion. Which script achieves this?

hard

A. for i in {2..10..2}; do echo $i; done

B. for i in {1..10}; do if [ $i % 2 == 0 ]; then echo $i; fi; done

C. for i in {2..10}; do echo $((i*2)); done

D. for i in {2..10..3}; do echo $i; done

Solution

1. Step 1: Understand brace expansion with step

   Brace expansion supports {start..end..step}, so {2..10..2} generates even numbers 2,4,6,8,10.

2. Step 2: Check other options

   B uses [ ] test which performs string comparison, not arithmetic modulo, so never prints evens; C multiplies numbers incorrectly to 4,6,8,10,12,14,16,18,20; D steps by 3, not 2.

3. Final Answer:

   for i in {2..10..2}; do echo $i; done -> Option A

4. Quick Check:

   Use {start..end..step} for stepped ranges [OK]

Hint: Use {start..end..step} to loop with steps in Bash [OK]

Common Mistakes:

• Not using step in brace expansion
• Multiplying loop variable instead of stepping
• Using wrong step size