Reading files line by line (while read) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this script reading a file line by line?

Consider a file named colors.txt with the following content:

red
green
blue

What will be the output of this script?

while read line; do
echo "$line"
done < colors.txt

Bash Scripting

while read line; do
echo "$line"
done < colors.txt

A

red
green
blue

B red green blue

C

eulb
neerg
der

D

ed
green
blue

💡 Hint

Think about how read reads each line and how echo prints it.

The script reads each line from the file and prints it on its own line. Each echo adds a newline, so the output ends with a newline.

💻 Command Output

intermediate

What happens if you use a pipe with while read loop?

Given the same colors.txt file, what will this script output?

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

Bash Scripting

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

A red green blue

B

red
green
blue

C No output

D

eulb
neerg
der

💡 Hint

Pipes send the file content to the loop line by line.

The pipe sends the file content line by line to the loop, which prints each line.

💻 Command Output

advanced

What error occurs with this incorrect while read syntax?

What error or output results from running this script?

while read line
  echo "$line"
done < colors.txt

Bash Scripting

while read line
  echo "$line"
done < colors.txt

A Syntax error: 'do' expected

B Prints all lines correctly

C No output

D Runtime error: file not found

💡 Hint

Check the syntax for the while loop in bash.

The 'do' keyword is required after the while condition to start the loop body.

🚀 Application

advanced

How to count lines in a file using while read loop?

Which script correctly counts the number of lines in colors.txt using a while read loop?

A

count=0
while read line; do
  count=$count + 1
done < colors.txt
echo $count

B

count=0
while read line; do
  count++
done < colors.txt
echo $count

C

count=0
while read line; do
  count=$((count + 1))
done < colors.txt
echo $count

D

count=0
while read line; do
  let count+1
done < colors.txt
echo $count

💡 Hint

Use arithmetic expansion $(( )) to increment variables in bash.

Only option C correctly increments the count variable using $((count + 1)). Others have syntax errors or do not update count properly.

🧠 Conceptual

expert

Why does this while read loop skip the last line sometimes?

Consider this script:

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

If file.txt does not end with a newline character, what happens to the last line and why?

A All lines print correctly regardless of newline

B The last line is printed twice due to buffering

C The script crashes with an error about missing newline

D The last line is skipped because read expects a newline to finish reading a line

💡 Hint

Think about how the read command detects line endings.

The read command reads until a newline. If the last line lacks a newline, read may not process it, causing it to be skipped.