sed substitution in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to replace the first occurrence of 'apple' with 'orange' in the input text.

Linux CLI

sed '[1]/apple/orange/' file.txt

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

Ad

By

Cs

Dp

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'y' instead of 's' which is for transliteration, not substitution.

Using 'd' which deletes lines, not substitutes text.

The 's' command in sed is used for substitution. Here, it replaces 'apple' with 'orange'.

2fill in blank

medium

Complete the code to replace all occurrences of 'cat' with 'dog' in the input text.

Linux CLI

sed '[1]/cat/dog/g' file.txt

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

As

Bd

Cy

Dp

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the 'g' flag, which replaces only the first occurrence per line.

Using 'd' which deletes lines instead of substituting text.

The 's' command with the 'g' flag replaces all occurrences of 'cat' with 'dog' in each line.

3fill in blank

hard

Fix the error in the sed command to replace 'blue' with 'red' only on lines containing 'sky'.

Linux CLI

sed '/sky/ [1] blue/red/' file.txt

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

Ad

Bs

Cp

Dy

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'd' which deletes lines instead of substituting text.

Omitting the 's' command causing syntax error.

The substitution command 's' must be used after the address '/sky/' to replace 'blue' with 'red' only on matching lines.

4fill in blank

hard

Fill both blanks to replace 'dog' with 'cat' only on lines starting with 'Pet'.

Linux CLI

sed '[1]/^Pet/ [2] dog/cat/' file.txt

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

A-n

Bs

Dp

Attempts:

3 left

💡 Hint

Common Mistakes

Not using '-n' causes all lines to print, not just modified ones.

Using 'p' instead of 's' for substitution.

The '-n' option suppresses automatic printing, and 's' performs substitution on lines starting with 'Pet'.

5fill in blank

hard

Fill all three blanks to replace 'apple' with 'orange' globally and print only changed lines.

Linux CLI

sed '[1]' file.txt | sed '[2]/apple/[3]/orange/gp'

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

A-n

Cs

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting '-n' causes all lines to print.

Using 'd' or 'p' incorrectly instead of 's' for substitution.

The first sed suppresses output with '-n'. The second sed uses '-n' and 's' with 'gp' to substitute globally and print changed lines.

Practice

1. What does the sed command sed 's/cat/dog/' file.txt do?

easy

A. Replaces the first occurrence of 'cat' with 'dog' on each line of file.txt

B. Replaces all occurrences of 'cat' with 'dog' in the entire file.txt

C. Deletes all lines containing 'cat' in file.txt

D. Prints lines containing 'dog' from file.txt

Solution

1. Step 1: Understand the sed substitution syntax

   The command sed 's/cat/dog/' file.txt uses s/pattern/replacement/ which replaces the first match per line.

2. Step 2: Apply the command to the file

   It replaces only the first 'cat' found on each line with 'dog', not all occurrences or lines.

3. Final Answer:

   Replaces the first occurrence of 'cat' with 'dog' on each line of file.txt -> Option A

4. Quick Check:

   sed s/pattern/replacement/ replaces first match per line [OK]

Hint: No 'g' flag means only first match per line replaced [OK]

Common Mistakes:

• Thinking all matches are replaced without 'g'
• Confusing substitution with deletion
• Assuming it prints only matching lines

2. Which of the following is the correct syntax to replace all occurrences of 'apple' with 'orange' using sed?

easy

A. sed 's/apple/orange/' file.txt

B. sed 's/apple/orange/g' file.txt

C. sed 's/apple/orange/g;' file.txt

D. sed 's/apple/orange/gp' file.txt

Solution

1. Step 1: Identify the flag for global replacement

   The 'g' flag after the substitution pattern tells sed to replace all occurrences on each line.

2. Step 2: Check syntax correctness

   sed 's/apple/orange/g' file.txt uses sed 's/apple/orange/g' which is the correct syntax without extra characters.

3. Final Answer:

   sed 's/apple/orange/g' file.txt -> Option B

4. Quick Check:

   'g' flag means replace all matches per line [OK]

Hint: Add 'g' after last slash to replace all matches [OK]

Common Mistakes:

• Omitting the 'g' flag for all replacements
• Adding extra semicolons inside quotes
• Using 'gp' which is invalid here

3. What is the output of this command if input.txt contains:

apple apple banana
banana apple apple

sed 's/apple/orange/' input.txt?

medium

A. orange orange banana
banana orange orange

B. orange apple banana
banana apple apple

C. orange apple banana
banana orange apple

D. apple apple banana
banana apple apple

Solution

1. Step 1: Understand sed substitution without 'g'

   Without 'g', only the first 'apple' on each line is replaced by 'orange'.

2. Step 2: Apply substitution line by line

   Line 1: 'apple apple banana' becomes 'orange apple banana'. Line 2: 'banana apple apple' becomes 'banana orange apple'.

3. Final Answer:

   orange apple banana banana orange apple -> Option C

4. Quick Check:

   First match per line replaced only [OK]

Hint: No 'g' means only first match per line changes [OK]

Common Mistakes:

• Replacing all 'apple' without 'g'
• Replacing none due to misunderstanding
• Confusing line order or content

4. Identify the error in this sed command: sed 's/hello/world/g file.txt'

medium

A. File name should come before the command

B. Incorrect delimiter used

C. Missing 'g' flag for global replacement

D. Missing closing quote after 'g'

Solution

1. Step 1: Check the quotes in the command

   The command has an opening single quote before s/hello/world/g but no closing quote after 'g'.

2. Step 2: Confirm correct placement of quotes and arguments

   The file name should be outside the quotes. The missing closing quote causes syntax error.

3. Final Answer:

   Missing closing quote after 'g' -> Option D

4. Quick Check:

   Quotes must enclose entire sed expression [OK]

Hint: Always close quotes around sed expression [OK]

Common Mistakes:

• Placing file name inside quotes
• Forgetting closing quote
• Confusing delimiter with quotes

5. You want to replace all occurrences of 'foo' with 'bar' only on lines containing 'baz' in data.txt. Which command achieves this?

hard

A. sed '/baz/ s/foo/bar/g' data.txt

B. sed 's/foo/bar/g /baz/' data.txt

C. sed 's/foo/bar/g' data.txt | grep baz

D. sed '/foo/ s/baz/bar/g' data.txt

Solution

1. Step 1: Understand address restriction in sed

   Using /baz/ s/foo/bar/g applies substitution only on lines matching 'baz'.

2. Step 2: Verify command correctness

   sed '/baz/ s/foo/bar/g' data.txt correctly restricts substitution to lines with 'baz' and replaces all 'foo' with 'bar'.

3. Final Answer:

   sed '/baz/ s/foo/bar/g' data.txt -> Option A

4. Quick Check:

   Address before command limits lines affected [OK]

Hint: Use /pattern/ before s/// to limit lines [OK]

Common Mistakes:

• Placing substitution after file name
• Using grep after sed instead of address
• Mixing patterns in wrong order