Why file I/O is core to scripting in Bash Scripting - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read the contents of a file named 'data.txt' and display it.

Bash Scripting

cat [1]

Drag options to blanks, or click blank then click option'

Aoutput.txt

Binput.txt

Cfile.txt

Ddata.txt

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong file name.

Forgetting to specify the file name after 'cat'.

The cat command reads and displays the contents of the specified file. Here, we want to read 'data.txt'.

2fill in blank

medium

Complete the code to write the text 'Hello World' into a file named 'greeting.txt'.

Bash Scripting

echo "Hello World" > [1]

Drag options to blanks, or click blank then click option'

Agreeting.txt

Boutput.txt

Chello.txt

Dmessage.txt

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong file name.

Using the append operator >> instead of overwrite >.

The echo command outputs text. Using > redirects this output into the specified file. Here, we want to write into 'greeting.txt'.

3fill in blank

hard

Fix the error in the code to append the text 'New line' to the file 'log.txt'.

Bash Scripting

echo "New line" [1] log.txt

Drag options to blanks, or click blank then click option'

A|

B>

C>>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using > which overwrites the file.

Using input redirection < or pipe | incorrectly.

The >> operator appends text to a file without overwriting existing content. Using > would overwrite the file.

4fill in blank

hard

Fill both blanks to create a script that reads 'input.txt', filters lines containing 'error', and writes them to 'errors.log'.

Bash Scripting

grep [1] [2] > errors.log

Drag options to blanks, or click blank then click option'

A"error"

Binput.txt

Coutput.txt

D"warning"

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong pattern or file name.

Confusing input and output files.

The grep command searches for a pattern in a file. Here, we search for the word 'error' in 'input.txt' and redirect the matching lines to 'errors.log'.

5fill in blank

hard

Fill all three blanks to create a script that counts lines in 'data.csv' containing the word 'success' and saves the count to 'count.txt'.

Bash Scripting

grep [1] [2] | wc -l > [3]

Drag options to blanks, or click blank then click option'

A"success"

Bdata.csv

Ccount.txt

Derrors.log

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong file names.

Forgetting to redirect output to the count file.

This command searches for 'success' in 'data.csv', counts the matching lines with wc -l, and writes the count to 'count.txt'.

Practice

1. Why is file input/output (I/O) important in bash scripting?

easy

A. It makes scripts run faster by using less memory.

B. It allows scripts to read from and write to files, automating tasks.

C. It helps scripts connect to the internet automatically.

D. It prevents scripts from crashing on errors.

Solution

1. Step 1: Understand file I/O purpose

   File I/O lets scripts handle data stored in files, such as logs or reports.

2. Step 2: Connect file I/O to automation

   By reading and writing files, scripts can automate many tasks involving data processing.

3. Final Answer:

   It allows scripts to read from and write to files, automating tasks. -> Option B

4. Quick Check:

   File I/O = Automate file data handling [OK]

Hint: File I/O means reading/writing files in scripts [OK]

Common Mistakes:

• Confusing file I/O with internet access
• Thinking file I/O speeds up script execution
• Assuming file I/O prevents all script errors

2. Which of the following is the correct way to redirect the output of a command to a file in bash?

easy

A. command |> output.txt

B. command >> output.txt <

C. command < output.txt

D. command > output.txt

Solution

1. Step 1: Identify output redirection syntax

   In bash, using > after a command sends its output to a file, overwriting it.

2. Step 2: Check other options for correctness

   > is correct; >> appends, < reads input, | pipes output, so only > fits the question.

3. Final Answer:

   command > output.txt -> Option D

4. Quick Check:

   Output redirection uses > [OK]

Hint: Use > to write output to a file, overwriting it [OK]

Common Mistakes:

• Using < instead of > for output
• Confusing >> (append) with > (overwrite)
• Using invalid symbols like |>

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

echo "Hello" > output.txt
echo "World" >> output.txt

medium

A. Hello
World

B. World

C. Hello

D. HelloWorld

Solution

1. Step 1: Analyze first echo command

   The first echo writes "Hello" to output.txt, overwriting any existing content.

2. Step 2: Analyze second echo command

   The second echo appends "World" to output.txt, adding it on a new line.

3. Final Answer:

   Hello World -> Option A

4. Quick Check:

   First overwrite, then append with newline [OK]

Hint: > overwrites file, >> appends with newline [OK]

Common Mistakes:

• Thinking >> overwrites instead of appends
• Ignoring newline added by echo
• Assuming output is just 'Hello' or 'World'

4. Identify the error in this script that tries to read from a file and print its content:

cat < input.txt

medium

A. The command should be 'cat >> input.txt' to append content.

B. The file name should be after the command without <, like 'cat > input.txt'.

C. The input redirection < is unnecessary; use 'cat input.txt' instead.

D. The script needs quotes around the file name.

Solution

1. Step 1: Understand cat command usage

   cat reads and prints file content when given the filename as an argument.

2. Step 2: Check input redirection usage

   Using < input.txt is valid but redundant here; 'cat input.txt' is simpler and standard.

3. Final Answer:

   The input redirection < is unnecessary; use 'cat input.txt' instead. -> Option C

4. Quick Check:

   cat filename is simpler than cat < filename [OK]

Hint: Use 'cat filename' to read files, not input redirection [OK]

Common Mistakes:

• Confusing input redirection with output redirection
• Using > or >> instead of < for input
• Adding unnecessary quotes around filename

5. You want to create a script that reads a list of usernames from users.txt and writes a greeting for each user into greetings.txt. Which script snippet correctly does this?

hard

A. while read user; do echo "Hello, $user!" >> greetings.txt; done < users.txt

B. for user in users.txt; do echo "Hello, $user!" > greetings.txt; done

C. cat users.txt | echo "Hello, $user!" > greetings.txt

D. echo "Hello, $(cat users.txt)!" > greetings.txt

Solution

1. Step 1: Understand reading lines from a file

   The 'while read user; do ... done < users.txt' reads each line (username) from users.txt correctly.

2. Step 2: Check writing greetings

   Inside the loop, echo appends a greeting line to greetings.txt for each user.

3. Final Answer:

   while read user; do echo "Hello, $user!" >> greetings.txt; done < users.txt -> Option A

4. Quick Check:

   Loop reads lines and appends greetings [OK]

Hint: Use while read loop with input redirection and append >> [OK]

Common Mistakes:

• Using for loop incorrectly on filename instead of lines
• Overwriting greetings.txt inside loop instead of appending
• Misusing cat with echo without looping