for loop with range ({1..10}) in Bash Scripting

Introduction

A for loop with a range lets you repeat commands a set number of times easily.

When you want to run a task 10 times in a row.

When you need to process files numbered from 1 to 10.

When you want to print numbers from 1 to 10.

When automating repetitive steps in a script.

When counting or iterating over a fixed sequence of numbers.

Syntax

Bash Scripting

for i in {1..10}
do
  commands using $i
 done

The numbers inside {1..10} define the start and end of the range.

Each loop step sets variable i to the next number in the range.

Examples

Prints numbers 1 to 5 with the word 'Number' before each.

Bash Scripting

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

Counts down from 10 to 1.

Bash Scripting

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

Prints even numbers from 2 to 8 using a step of 2.

Bash Scripting

for i in {2..8..2}
do
  echo $i
done

Sample Program

This script counts from 1 to 10 and prints each number with 'Counting:'.

Bash Scripting

#!/bin/bash
for i in {1..10}
do
  echo "Counting: $i"
done

Important Notes

Make sure to use double quotes around variables to avoid word splitting.

The range {1..10} works in Bash version 3 and above.

You can change the step by adding a third number like {1..10..2}.

Summary

Use for loops with {start..end} to repeat commands over a number range.

The loop variable changes each time from start to end.

You can customize the range and step size easily.

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