Linux `sed` Command Quiz

 ### 🐧 Top 25 Linux `sed` Command Quiz — With Answers

## 1. Which option enables extended regular expressions in GNU sed?

A) -i

B) -E

C) -n

D) -f

✅ Answer: B) -E

## 2. What does the -n option do?

A) Number lines

B) Suppress automatic printing

C) Edit files

D) Enable regex

✅ Answer: B) Suppress automatic printing

## 3. What does the -i option do?

A) Ignore case

B) Edit files in place

C) Insert text

D) Print line numbers

✅ Answer: B) Edit files in place

## 4. Which command replaces the first occurrence of 'old' with 'new'?

A) sed 's/old/new/' file

B) sed 'd/old/new/' file

C) sed 'p/old/new/' file

D) sed 'r/old/new/' file

✅ Answer: A) sed 's/old/new/' file

## 5. What does the g flag mean in sed substitution?

A) Go to line

B) Global replacement

C) Group lines

D) Generate output

✅ Answer: B) Global replacement

## 6. What is the output?

echo 'hello world' | sed 's/world/Linux/'

A) hello world

B) Linux world

C) hello Linux

D) Linux

✅ Answer: C) hello Linux

## 7. Which sed command deletes line 3?

A) sed '3p' file

B) sed '3d' file

C) sed '3r' file

D) sed '3i' file

✅ Answer: B) sed '3d' file

## 8. What does sed -n '2p' file display?

A) All lines

B) Only line 2

C) Lines 2 and 3

D) Only the last line

✅ Answer: B) Only line 2

## 9. Which command prints line numbers?

A) sed -n 'l' file

B) sed '=' file

C) sed 'n' file

D) sed -n 'N' file

✅ Answer: B) sed '=' file

## 10. What does the -e option specify?

A) File encoding

B) A sed script/expression

C) End of file

D) Extended deletion

✅ Answer: B) A sed script/expression

## 11. Which option reads commands from a script file?

A) -f

B) -r

C) -c

D) -s

✅ Answer: A) -f

## 12. What does sed '2,4d' file do?

A) Deletes lines 2 through 4

B) Deletes only line 2

C) Prints lines 2 through 4

D) Replaces lines

✅ Answer: A) Deletes lines 2 through 4

## 13. Which command replaces all occurrences of 'cat' with 'dog'?

A) sed 's/cat/dog/' file

B) sed 's/cat/dog/g' file

C) sed 'r/cat/dog/g' file

D) sed 'd/cat/dog/g' file

✅ Answer: B) sed 's/cat/dog/g' file

## 14. What does the p command do?

A) Pause

B) Print pattern space

C) Parse file

D) Previous line

✅ Answer: B) Print pattern space

## 15. What is the output?

echo 'Linux' | sed 'y/L/l/'

A) linux

B) Linux

C) LINUX

D) Error

✅ Answer: A) linux

## 16. Which command removes blank lines?

A) sed '/^$/d' file

B) sed '/blank/d' file

C) sed 'blank' file

D) sed '/^$/p' file

✅ Answer: A) sed '/^$/d' file

## 17. What does the q command do?

A) Queries input

B) Quits sed

C) Quotes text

D) Queues lines

✅ Answer: B) Quits sed

## 18. Which command inserts 'Hello' before line 2?

A) sed '2a Hello' file

B) sed '2i Hello' file

C) sed '2c Hello' file

D) sed '2p Hello' file

✅ Answer: B) sed '2i Hello' file

## 19. Which command appends 'Hello' after line 2?

A) sed '2i Hello' file

B) sed '2a Hello' file

C) sed '2d Hello' file

D) sed '2r Hello' file

✅ Answer: B) sed '2a Hello' file

## 20. What does sed 's/[0-9]//g' file do?

A) Removes all digits

B) Removes all letters

C) Adds digits

D) Prints only digits

✅ Answer: A) Removes all digits

## 21. What does the c command do?

A) Copies lines

B) Changes/replaces selected lines

C) Counts lines

D) Comments lines

✅ Answer: B) Changes/replaces selected lines

## 22. Which flag makes substitution case-insensitive in GNU sed?

A) -i

B) i (or I)

C) -n

D) -E

✅ Answer: B) i (or I)

Example:

sed 's/linux/unix/i' file

## 23. What does sed -n '1~2p' file do in GNU sed?

A) Prints every line

B) Prints odd-numbered lines starting from 1

C) Prints even-numbered lines

D) Deletes odd lines

✅ Answer: B) Prints odd-numbered lines starting from 1

## 24. Which sed command reads and inserts file content after a matching line?

A) r

B) w

C) e

D) a

✅ Answer: A) r

## 25. What does the w command do?

A) Writes selected pattern space to a file

B) Waits for input

C) Wraps lines

D) Writes to standard input

✅ Answer: A) Writes selected pattern space to a file

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