Writing to files (echo, printf) in Bash Scripting - Mini Project: Build & Apply

Writing to files using echo and printf in Bash

📖 Scenario: You are creating a simple log file for a small script that tracks daily tasks. You want to write messages to a file to keep a record.

🎯 Goal: Learn how to write text lines to a file using echo and printf commands in Bash scripting.

📋 What You'll Learn

Create a text file with initial content using echo

Add a configuration variable for the filename

Use printf to format and append text to the file

Display the final content of the file

💡 Why This Matters

🌍 Real World

Writing logs or reports to files is common in automation scripts to keep track of actions or errors.

💼 Career

Knowing how to write and append to files is essential for scripting tasks in system administration, DevOps, and automation roles.

1

Create a file with initial content using echo

Use echo to write the exact text "Daily Tasks Log" into a file named tasks.txt. Overwrite the file if it exists.

Bash Scripting

# Use echo to write 'Daily Tasks Log' into tasks.txt
# Your code here

Hint

Use echo "text" > filename to write text to a file, replacing any existing content.

2

Add a variable for the filename

Create a variable called file and set it to the string "tasks.txt".

Bash Scripting

echo "Daily Tasks Log" > tasks.txt
# Create a variable called file with value "tasks.txt"
# Your code here

Hint

Use file="tasks.txt" to assign the filename to a variable.

3

Append formatted text using printf

Use printf to append the exact line "- Task 1: Write script" to the file stored in the variable file. Use the append operator >>.

Bash Scripting

echo "Daily Tasks Log" > tasks.txt
file="tasks.txt"
# Use printf to append '- Task 1: Write script' to the file variable
# Your code here

Hint

Use printf "text\n" >> "$file" to append a line with a newline character.

4

Display the content of the file

Use cat to display the content of the file stored in the variable file.

Bash Scripting

echo "Daily Tasks Log" > tasks.txt
file="tasks.txt"
printf "- Task 1: Write script\n" >> "$file"
# Display the content of the file variable
# Your code here

Hint

Use cat "$file" to show the file content.

Practice

1. Which command in bash writes the text Hello World to a file named greeting.txt and adds a newline automatically?

easy

A. echo "Hello World" > greeting.txt

B. printf "Hello World" > greeting.txt

C. echo -n "Hello World" > greeting.txt

D. printf "Hello World\n" > greeting.txt

Solution

1. Step 1: Understand echo behavior

   The echo command prints text and adds a newline by default.

2. Step 2: Compare with printf

   printf requires explicit newline characters to add a newline.

3. Final Answer:

   echo "Hello World" > greeting.txt -> Option A

4. Quick Check:

   echo adds newline automatically = A [OK]

Hint: Use echo for quick writes with newline [OK]

Common Mistakes:

• Using printf without \n misses newline
• Using echo -n suppresses newline
• Confusing > and >> operators

2. Which of the following is the correct syntax to append the line Log entry to a file log.txt using printf?

easy

A. printf "Log entry" >> log.txt

B. printf -n "Log entry" >> log.txt

C. printf "Log entry\n" >> log.txt

D. printf -e "Log entry" >> log.txt

Solution

1. Step 1: Understand printf newline requirement

   printf does not add newline automatically; you must include \n explicitly.

2. Step 2: Check append operator

   >> appends to the file without overwriting.

3. Final Answer:

   printf "Log entry\n" >> log.txt -> Option C

4. Quick Check:

   printf needs \n for newline + append with >> = C [OK]

Hint: Always add \n with printf to get a new line [OK]

Common Mistakes:

• Forgetting \n causes no newline
• Using > instead of >> overwrites file
• Using invalid printf flags like -n or -e

3. What will be the content of file.txt after running this script?

echo "Line1" > file.txt
printf "Line2\n" >> file.txt
echo -n "Line3" >> file.txt

medium

A. Line1\nLine2Line3

B. Line1\nLine2\nLine3\n

C. Line1Line2Line3

D. Line1\nLine2\nLine3

Solution

1. Step 1: Analyze echo "Line1" > file.txt

   This writes "Line1" plus newline to file.txt, overwriting existing content.

2. Step 2: Analyze printf "Line2\n" >> file.txt

   This appends "Line2" plus newline to file.txt.

3. Step 3: Analyze echo -n "Line3" >> file.txt

   This appends "Line3" without newline to file.txt.

4. Final Answer:

   Line1\nLine2\nLine3 -> Option D

5. Quick Check:

   echo adds newline, printf adds newline, echo -n no newline = D [OK]

Hint: Remember echo -n skips newline, printf needs explicit \n [OK]

Common Mistakes:

• Assuming echo -n adds newline
• Forgetting printf needs \n
• Confusing overwrite (>) and append (>>)

4. The following script is intended to write two lines to output.txt but only writes one line. What is the error?

echo "First line" > output.txt
printf "Second line" > output.txt

medium

A. printf needs \n to add newline

B. Second command overwrites the file instead of appending

C. echo should use >> to append

D. Missing quotes around Second line

Solution

1. Step 1: Check file redirection operators

   The first command uses > which creates or overwrites output.txt with "First line".

2. Step 2: Check second command redirection

   The second command also uses > which overwrites output.txt, replacing previous content.

3. Step 3: Correct approach

   To keep both lines, second command should use >> to append instead of overwrite.

4. Final Answer:

   Second command overwrites the file instead of appending -> Option B

5. Quick Check:

   Using > twice overwrites file = D [OK]

Hint: Use >> to append, > overwrites file [OK]

Common Mistakes:

• Thinking \n missing causes no second line
• Confusing > and >> operators
• Assuming echo always appends

5. You want to create a file report.txt with exactly two lines:
"Summary:"
"All tests passed"
Which script snippet correctly creates this file with proper newlines and no extra blank lines?

hard

A. printf "Summary:\nAll tests passed\n" > report.txt

B. echo "Summary:" > report.txt && echo "All tests passed" > report.txt

C. echo -n "Summary:\nAll tests passed" > report.txt

D. printf "Summary:" > report.txt && printf "All tests passed" >> report.txt

Solution

1. Step 1: Check echo commands in echo "Summary:" > report.txt && echo "All tests passed" > report.txt

   echo "Summary:" > report.txt && echo "All tests passed" > report.txt uses echo twice with > redirection, so the second command overwrites the first line.

2. Step 2: Check printf commands in printf "Summary:\nAll tests passed\n" > report.txt

   printf "Summary:\nAll tests passed\n" > report.txt uses printf with explicit \n for newlines, creating exactly two lines with no extra blank lines.

3. Step 3: Analyze Options C and D

   echo -n "Summary:\nAll tests passed" > report.txt uses echo -n which suppresses newlines and includes literal \n, so no actual new lines appear. printf "Summary:" > report.txt && printf "All tests passed" >> report.txt uses printf without \n, so lines run together.

4. Final Answer:

   printf "Summary:\nAll tests passed\n" > report.txt -> Option A

5. Quick Check:

   printf with explicit \n creates exact lines = B [OK]

Hint: Use printf with \n for precise multi-line output [OK]

Common Mistakes:

• Using echo -n with \n prints literal \n
• Forgetting \n in printf causes no new lines
• Using > and >> inconsistently