Reading files line by line (while read) in Bash Scripting - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read a file line by line using a while loop.

Bash Scripting

while [1] read line; do
  echo "$line"
done < file.txt

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

Ado

Bcat

CIFS=

Dfor

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'for' loop instead of 'while' to read lines

Not setting IFS, causing trimming of spaces

Using 'cat' incorrectly inside the while loop

Setting IFS= before read ensures that leading/trailing whitespace is preserved when reading each line.

2fill in blank

medium

Complete the code to read a file named 'data.txt' line by line and print each line.

Bash Scripting

while IFS= read [1]; do
  echo "$line"
done < data.txt

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

Atext

Bline

Cfile

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names that do not match the echo statement

Using reserved words as variable names

The variable 'line' is commonly used to store each line read from the file.

3fill in blank

hard

Fix the error in the code to correctly read lines from 'input.txt'.

Bash Scripting

while IFS= read line; do
  echo "$line"
done < [1]

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Ainput.txt

Bfile.txt

Coutput.txt

Ddata.txt

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong filename in the input redirection

Missing the '<' symbol before the filename

The file to read from must be 'input.txt' as intended by the code.

4fill in blank

hard

Fill both blanks to read 'myfile.txt' line by line and count lines longer than 5 characters.

Bash Scripting

count=0
while [1] read line; do
  if [ ${#line} [2] 5 ]; then
    count=$((count + 1))
  fi
done < myfile.txt
echo $count

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

AIFS=

B>

C-gt

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' instead of '-gt' in test brackets

Not setting IFS= causing trimmed lines

Setting IFS= preserves spaces. The test uses '-gt' to check if length is greater than 5.

5fill in blank

hard

Fill all three blanks to create a dictionary of word lengths for words longer than 3 characters.

Bash Scripting

declare -A lengths
for word in apple banana cat dog elephant; do
  if [ ${#word} [1] 3 ]; then
    lengths[[2]]=[3]
  fi
done
for k in "${!lengths[@]}"; do
  echo "$k: ${lengths[$k]}"
done

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

A-gt

Bword

C${#word}

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '-gt' for numeric comparison

Using wrong keys or values in the associative array

Use '-gt' to check length > 3, use 'word' as key, and '${#word}' as value for length.

Practice

1. What does the command while IFS= read -r line; do echo "$line"; done < file.txt do in a bash script?

easy

A. Deletes the contents of file.txt.

B. Reads the entire file at once and prints it.

C. Writes each line of file.txt to a new file.

D. Reads the file file.txt line by line and prints each line.

Solution

1. Step 1: Understand the while read loop

   The loop reads input line by line from the redirected file file.txt.

2. Step 2: Check the action inside the loop

   Each line read is stored in variable line and printed with echo.

3. Final Answer:

   Reads the file file.txt line by line and prints each line. -> Option D

4. Quick Check:

   Line-by-line reading = A [OK]

Hint: Remember: while read loops read files line by line [OK]

Common Mistakes:

• Thinking it reads the whole file at once
• Confusing input redirection with output
• Ignoring the role of IFS= and -r

2. Which of the following is the correct syntax to read a file line by line in bash?

easy

A. while read line; do echo $line; done < file.txt

B. while read -r line; do echo $line; done > file.txt

C. while read line; do echo $line; done >> file.txt

D. while read line; do echo $line; done | file.txt

Solution

1. Step 1: Identify input redirection for reading

   The correct way to read from a file is using input redirection: < file.txt.

2. Step 2: Check the loop syntax

   while read line; do ... done is the standard loop to read lines.

3. Final Answer:

   while read line; do echo $line; done < file.txt -> Option A

4. Quick Check:

   Input redirection with < = C [OK]

Hint: Use < file.txt to feed file lines into the loop [OK]

Common Mistakes:

• Using output redirection (>) instead of input (<)
• Piping file name instead of redirecting input
• Missing the -r option to prevent backslash escapes

3. What will be the output of this script if file.txt contains:

apple
banana
cherry

Script:

while IFS= read -r line; do echo "Fruit: $line"; done < file.txt

medium

A. Fruit: apple
Fruit: banana
Fruit: cherry

B. apple
banana
cherry

C. Fruit: apple banana cherry

D. Syntax error

Solution

1. Step 1: Understand the loop reading each line

   The loop reads each line from file.txt separately.

2. Step 2: Check the echo command

   Each line is printed prefixed with "Fruit: ".

3. Final Answer:

   Fruit: apple Fruit: banana Fruit: cherry -> Option A

4. Quick Check:

   Line prefixing with echo = B [OK]

Hint: Each loop iteration prints one line with prefix [OK]

Common Mistakes:

• Expecting all lines printed on one line
• Ignoring the prefix in echo
• Confusing input and output redirection

4. Identify the error in this script snippet:

while read line; do echo $line; done file.txt

medium

A. Echo command syntax is wrong

B. Incorrect variable name used

C. Missing input redirection operator < before file.txt

D. Missing semicolon after read

Solution

1. Step 1: Check how the file is provided to the loop

   The file must be redirected as input using < file.txt, not as an argument.

2. Step 2: Confirm syntax correctness

   The rest of the syntax is correct; variable and echo usage are fine.

3. Final Answer:

   Missing input redirection operator < before file.txt -> Option C

4. Quick Check:

   Input redirection needed = D [OK]

Hint: Use < file.txt to feed file lines, not argument [OK]

Common Mistakes:

• Passing filename as argument instead of redirecting input
• Forgetting semicolon after read (optional here)
• Misusing echo syntax

5. You want to read a file line by line and skip empty lines. Which script snippet correctly does this?

hard

A. while read line; do echo "$line"; done < file.txt | grep '^$'

B. while IFS= read -r line; do if [[ -n $line ]]; then echo "$line"; fi; done < file.txt

C. cat file.txt | while read line; do echo "$line"; done

D. while IFS= read -r line; do echo "$line"; done < file.txt

Solution

1. Step 1: Understand skipping empty lines

   We need to check if the line is not empty using [[ -n $line ]].

2. Step 2: Confirm reading and condition

   while IFS= read -r line; do if [[ -n $line ]]; then echo "$line"; fi; done < file.txt reads lines safely and prints only non-empty lines inside the loop.

3. Final Answer:

   while IFS= read -r line; do if [[ -n $line ]]; then echo "$line"; fi; done < file.txt -> Option B

4. Quick Check:

   Condition inside loop filters empty lines = A [OK]

Hint: Use if [[ -n $line ]] inside loop to skip empty lines [OK]

Common Mistakes:

• Using external grep after loop (may lose variable scope)
• Not checking for empty lines inside the loop
• Using unnecessary cat command