sed (stream editor) basics in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to replace the word 'apple' with 'orange' in the file fruits.txt.

Linux CLI

sed '[1]' fruits.txt

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

As/apple/orange/g

Br/apple/orange/g

Cd/apple/orange/g

Di/apple/orange/g

Attempts:

3 left

💡 Hint

Common Mistakes

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

Forgetting the 'g' flag to replace all occurrences.

The 's' command in sed is used for substitution. 's/apple/orange/g' replaces all occurrences of 'apple' with 'orange'.

2fill in blank

medium

Complete the code to delete all lines containing the word 'banana' from the file fruits.txt.

Linux CLI

sed '/[1]/d' fruits.txt

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

Aorange

Bbanana

Capple

Dgrape

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong word inside the pattern.

Omitting the 'd' command to delete lines.

The command '/banana/d' tells sed to delete lines containing 'banana'.

3fill in blank

hard

Fix the error in the code to print only lines 2 to 4 from the file fruits.txt.

Linux CLI

sed -n '[1]p' fruits.txt

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

A2-4

B2;4

C2,4

D2.4

Attempts:

3 left

💡 Hint

Common Mistakes

Using a dash '-' instead of a comma ',' for range.

Using semicolon or dot which are invalid for ranges.

The correct range syntax in sed is '2,4' to specify lines 2 through 4.

4fill in blank

hard

Fill both blanks to replace the first occurrence of 'cat' with 'dog' only on lines containing 'pet' in the file animals.txt.

Linux CLI

sed '/[1]/s/[2]/dog/' animals.txt

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

Apet

Bcat

Cdog

Danimal

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the pattern and the word to replace.

Using 'dog' as the pattern to match instead of 'cat'.

The command '/pet/s/cat/dog/' replaces the first 'cat' with 'dog' on those lines.

5fill in blank

hard

Fill all three blanks to append the line 'End of file' after the last line of the file report.txt.

Linux CLI

sed '[1][2]\
[3]' report.txt

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

A$

Ba

CEnd of file

Di

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'i' instead of 'a' which inserts before the line.

Not using '$' to target the last line.

The command '$a\nEnd of file' (newline after 'a') tells sed to append 'End of file' after the last line ($) of the file.

Practice

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

easy

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

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

C. Prints only lines containing 'dog' from file.txt

D. Appends 'dog' at the end of each line containing 'cat' in file.txt

Solution

1. Step 1: Understand the substitution command

   The s/pattern/replacement/ syntax in sed replaces the first match of 'pattern' with 'replacement' on each line.

2. Step 2: Apply to the given command

   The command replaces the first occurrence of 'cat' with 'dog' on every line of file.txt.

3. Final Answer:

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

4. Quick Check:

   sed substitution = replace first match [OK]

Hint: Remember: s/pattern/replacement/ changes first match per line [OK]

Common Mistakes:

• Thinking it deletes lines instead of substituting
• Assuming it replaces all occurrences without 'g' flag
• Confusing printing lines with substitution

2. Which of the following is the correct syntax to delete all lines containing the word 'error' using sed?

easy

A. sed '/error/d' filename

B. sed 'd/error/' filename

C. sed 's/error/d/' filename

D. sed 'delete /error/' filename

Solution

1. Step 1: Identify the delete command syntax in sed

   To delete lines matching a pattern, the syntax is sed '/pattern/d'.

2. Step 2: Match the correct option

   sed '/error/d' filename uses sed '/error/d', which deletes lines containing 'error'. Other options have incorrect syntax.

3. Final Answer:

   sed '/error/d' filename -> Option A

4. Quick Check:

   Delete lines with pattern = /pattern/d [OK]

Hint: Use '/pattern/d' to delete matching lines in sed [OK]

Common Mistakes:

• Placing 'd' before the pattern
• Using substitution syntax instead of delete
• Writing 'delete' instead of 'd'

3. What is the output of the command echo 'apple banana apple' | sed 's/apple/orange/g'?

medium

A. orange banana orange

B. orange banana apple

C. apple banana apple

D. apple banana orange

Solution

1. Step 1: Understand the 'g' flag in substitution

   The 'g' flag means replace all occurrences of the pattern on each line, not just the first.

2. Step 2: Apply substitution to the input string

   All 'apple' words are replaced by 'orange', so 'apple banana apple' becomes 'orange banana orange'.

3. Final Answer:

   orange banana orange -> Option A

4. Quick Check:

   Substitute all matches with 'g' flag = replaced all [OK]

Hint: Add 'g' to replace all matches, not just first [OK]

Common Mistakes:

• Forgetting the 'g' flag replaces only first occurrence
• Confusing output with original input
• Misreading the pipe input

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

medium

A. No error; command is correct

B. Incorrect command; 's' cannot be used with text files

C. The pattern 'hello' is invalid

D. Missing delimiter after replacement text

Solution

1. Step 1: Check the substitution syntax

   The substitution command requires delimiters: s/pattern/replacement/. The final '/' is missing here.

2. Step 2: Identify the missing delimiter

   The command ends with 's/hello/goodbye' missing the closing '/' delimiter after 'goodbye'.

3. Final Answer:

   Missing delimiter after replacement text -> Option D

4. Quick Check:

   Substitution needs closing '/' delimiter [OK]

Hint: Check that substitution ends with '/' delimiter [OK]

Common Mistakes:

• Omitting the last '/' in substitution
• Assuming 's' can't be used on files
• Thinking pattern must be a regex error

5. You want to replace the word 'cat' with 'dog' only on lines 2 to 4 in a file named pets.txt. Which sed command achieves this?

hard

A. sed 's/cat/dog/ 2,4' pets.txt

B. sed '/2,4 s/cat/dog/' pets.txt

C. sed '2,4s/cat/dog/' pets.txt

D. sed 's/cat/dog/ 2-4' pets.txt

Solution

1. Step 1: Understand address range in sed

   To apply a command only on specific lines, use start,endcommand syntax, e.g., 2,4s/pattern/replacement/.

2. Step 2: Match the correct syntax

   sed '2,4s/cat/dog/' pets.txt correctly uses 2,4s/cat/dog/ to replace 'cat' with 'dog' on lines 2 to 4.

3. Final Answer:

   sed '2,4s/cat/dog/' pets.txt -> Option C

4. Quick Check:

   Use line range before command to limit sed action [OK]

Hint: Use 'start,end' before 's' to limit substitution lines [OK]

Common Mistakes:

• Placing line numbers after substitution command
• Using incorrect range syntax like '2-4'
• Adding slashes around line numbers