History command and search in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of history search with grep

What is the output of the following command sequence in a Linux shell where the history contains these commands:

1. ls -l
2. cd /var
3. ls -a
4. history

Command:
history | grep ls

Linux CLI

history | grep ls

A

  1  ls -l
  2  cd /var
  3  ls -a

B

ls -l
ls -a

C

  1  ls -l
  3  ls -a

D 2 cd /var

💡 Hint

The grep command filters lines containing 'ls' from the history output.

The history command lists all previous commands with their numbers. Grep filters lines containing 'ls'. Only commands 1 and 3 contain 'ls'.

💻 Command Output

intermediate

Effect of reverse search with Ctrl+R

If you press Ctrl+R in a Linux terminal and type 'git', what will happen?

A It opens the git manual page.

B It shows the most recent command in history containing 'git'.

C It deletes the last command from history.

D It clears the terminal screen.

💡 Hint

Ctrl+R is used for reverse search in command history.

Ctrl+R activates reverse incremental search. Typing 'git' finds the last command with 'git' in history.

📝 Syntax

advanced

Correct syntax for searching history with a pattern

Which command correctly searches the history for commands containing the word 'docker' and shows line numbers?

A history | grep docker

B grep docker history

C history grep docker

D history -search docker

💡 Hint

Use pipe to send history output to grep.

The history command outputs the list, which can be piped to grep to filter lines containing 'docker'.

🔧 Debug

advanced

Why does this history search command fail?

A user runs this command:
history | grep 'apt-get update'
But it returns no results, even though they ran 'sudo apt-get update' earlier. Why?

A Because the command in history includes 'sudo' and the search is for 'apt-get update' only.

B Because grep cannot search for strings with spaces.

C Because history does not store commands with sudo.

D Because the history command needs root privileges to show all commands.

💡 Hint

Check the exact text stored in history.

The command stored was 'sudo apt-get update', so searching for 'apt-get update' alone does not match.

🚀 Application

expert

Count how many unique commands contain 'ssh' in history

You want to find out how many unique commands in your history contain the string 'ssh'. Which command will give you the correct count?

A history | sort | grep ssh | uniq | wc -l

B history | grep ssh | uniq | wc -l

C history | grep ssh | wc -l

D history | grep ssh | sort | uniq | wc -l

💡 Hint

You need to filter, sort, remove duplicates, then count lines.

Piping history to grep filters lines with 'ssh'. Sorting is needed before uniq to remove duplicates correctly. Then wc -l counts lines.