stdout redirection (>, >>) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the content of the file after this command?

Assume file.txt initially contains:

Hello

What will be the content of file.txt after running:

echo "World" > file.txt

Linux CLI

echo "World" > file.txt

A Hello

B Hello\nWorld

C World

D World\nHello

💡 Hint

The single > operator overwrites the file content.

The > operator replaces the entire content of the file with the new output. So the file will only contain "World".

💻 Command Output

intermediate

What will be the content of the file after appending?

Assume file.txt initially contains:

Line1

What will be the content of file.txt after running:

echo "Line2" >> file.txt

Linux CLI

echo "Line2" >> file.txt

A Line2

B Line1\nLine2

C Line1

D Line2\nLine1

💡 Hint

The >> operator adds the output to the end of the file.

The >> operator appends the output to the existing file content, so the file will have both lines.

💻 Command Output

advanced

What is the output of this command sequence?

Given an empty file log.txt, what will be the content after running these commands?

echo "Start" > log.txt
 echo "Middle" >> log.txt
 echo "End" > log.txt

Linux CLI

echo "Start" > log.txt
 echo "Middle" >> log.txt
 echo "End" > log.txt

A End

B Start\nMiddle

C Start\nMiddle\nEnd

D Middle\nEnd

💡 Hint

The last command overwrites the file again.

The first command writes "Start", the second appends "Middle", but the last command overwrites the file with "End" only.

💻 Command Output

advanced

What error or output occurs here?

What happens if you run this command when readonly.txt is a read-only file?

echo "New content" > readonly.txt

Linux CLI

echo "New content" > readonly.txt

A Permission denied error

B New content is written to the file

C File is created with new content

D No output, command silently fails

💡 Hint

You need write permission to overwrite a file.

If the file is read-only, the shell cannot overwrite it and will show a permission denied error.

🧠 Conceptual

expert

How many lines will the file contain after this script?

Consider this script run in an empty directory:

for i in 1 2 3; do
  echo "Line $i" >> file.txt
  echo "Overwrite $i" > file.txt
 done

How many lines will file.txt have after the loop finishes?

Linux CLI

for i in 1 2 3; do
  echo "Line $i" >> file.txt
  echo "Overwrite $i" > file.txt
 done

A 0

B 3

C 6

D 1

💡 Hint

Each loop overwrites the file after appending.

Each loop first appends a line, then immediately overwrites the file with one line. After 3 loops, only the last overwrite remains, so the file has 1 line.

Practice

1. What does the command echo "Hello" > file.txt do in Linux?

easy

A. It writes "Hello" to file.txt, replacing any existing content.

B. It adds "Hello" to the end of file.txt without removing existing content.

C. It displays "Hello" on the screen without saving to a file.

D. It deletes file.txt if it exists.

Solution

1. Step 1: Understand the > operator

   The > operator redirects output to a file, replacing its content.

2. Step 2: Analyze the command effect

   echo "Hello" outputs "Hello" and > saves it to file.txt, overwriting old content.

3. Final Answer:

   It writes "Hello" to file.txt, replacing any existing content. -> Option A

4. Quick Check:

   > means overwrite file [OK]

Hint: Use > to overwrite file content, >> to append [OK]

Common Mistakes:

• Confusing > with >> and thinking it appends
• Believing output only shows on screen
• Assuming file is deleted

2. Which of the following commands correctly appends the text "Log entry" to a file named log.txt?

easy

A. echo "Log entry" < log.txt

B. echo "Log entry" > log.txt

C. echo "Log entry" >! log.txt

D. echo "Log entry" >> log.txt

Solution

1. Step 1: Identify append operator

   The >> operator appends output to the end of a file without deleting existing content.

2. Step 2: Match command with append operator

   Only echo "Log entry" >> log.txt uses >> correctly to append "Log entry" to log.txt.

3. Final Answer:

   echo "Log entry" >> log.txt -> Option D

4. Quick Check:

   >> means append output [OK]

Hint: Use >> to add text without erasing file [OK]

Common Mistakes:

• Using > which overwrites instead of appending
• Using < which is input redirection, not output
• Using invalid >! operator

3. Given the file content of data.txt is initially empty, what will be the content of data.txt after running these commands in order?

echo "First" > data.txt
echo "Second" >> data.txt
echo "Third" > data.txt

medium

A. Third

B. First\nSecond

C. Second\nThird

D. First\nSecond\nThird

Solution

1. Step 1: Analyze first command

   echo "First" > data.txt writes "First" to data.txt, replacing any content.

2. Step 2: Analyze second command

   echo "Second" >> data.txt appends "Second" after "First".

3. Step 3: Analyze third command

   echo "Third" > data.txt overwrites entire file with "Third" only.

4. Final Answer:

   Third -> Option A

5. Quick Check:

   Last > overwrites file content [OK]

Hint: Last > overwrites file, ignoring previous appends [OK]

Common Mistakes:

• Thinking >> always appends without overwrite
• Assuming all lines remain after last >
• Confusing ">" and ">>" effects

4. You want to append the output of date command to a file named times.log. Which command has an error and why?

A) date >> times.log
B) date > times.log
C) date >>> times.log
D) date >> times.log

medium

A. Correctly appends date output to times.log

B. Overwrites times.log with date output

C. Syntax error due to invalid operator >>>

D. gol.semit ot tuptuo etad sdneppa yltcerroC

Solution

1. Step 1: Check each redirection operator

   A uses >> (append), B uses > (overwrite), C uses >>> (invalid), D uses >> (valid).

2. Step 2: Identify invalid syntax

   Operator >>> is not valid in Linux shell, causing syntax error.

3. Final Answer:

   Syntax error due to invalid operator >>> -> Option C

4. Quick Check:

   >> is invalid operator [OK]

Hint: Only > and >> are valid output redirections [OK]

Common Mistakes:

• Using >>> instead of >>
• Thinking no space after >> is error
• Confusing > and >> effects

5. You have a script that logs errors to error.log. You want to keep all previous errors and add new ones each time the script runs. Which command should you use inside the script to save the error message "Error occurred" to the file without deleting old logs?

hard

A. echo "Error occurred" > error.log

B. echo "Error occurred" >> error.log

C. echo "Error occurred" >! error.log

D. echo "Error occurred" < error.log

Solution

1. Step 1: Understand logging requirement

   We want to keep old logs and add new errors, so appending is needed.

2. Step 2: Choose correct redirection operator

   > overwrites file, >> appends to file. So >> is correct to keep old content.

3. Final Answer:

   echo "Error occurred" >> error.log -> Option B

4. Quick Check:

   Use >> to append logs without deleting [OK]

Hint: Use >> to add logs, never > to avoid losing data [OK]

Common Mistakes:

• Using > which erases old logs
• Using < which is input redirection
• Using invalid >! operator