History command and search in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the history command do in Linux?

The history command shows a list of commands you have typed before in the terminal. It helps you see past commands to reuse or review them.

beginner

How do you search your command history interactively in Linux?

Press Ctrl + R to start a reverse search. Then type part of the command you want to find. The terminal will show matching commands from your history.

intermediate

What does the command !123 do in the Linux shell?

It runs the command numbered 123 from your history list. This lets you quickly repeat a past command by its history number.

beginner

Explain the use of !! in the Linux shell.

!! repeats the last command you typed. It is a quick way to run the previous command again without retyping it.

intermediate

How can you limit the number of commands shown by the history command?

Use history | tail -n N where N is the number of recent commands you want to see. For example, history | tail -n 10 shows the last 10 commands.

Which key combination starts a reverse search in the Linux command history?

A Ctrl + R

B Ctrl + S

C Ctrl + H

D Ctrl + L

Ctrl + R starts a reverse search to find commands in your history.

What does the command !ls do?

A Runs the last command starting with 'ls'

B Lists files in the current directory

C Shows the history of 'ls' commands

D Deletes the last 'ls' command from history

!ls runs the most recent command that starts with 'ls' from your history.

How do you repeat the last command you typed?

A Ctrl + C

B !!

C history

D !1

!! repeats the last command entered.

What does history 5 show?

A The first 5 commands typed

B All commands except the last 5

C The last 5 commands typed

D The 5th command in history

history 5 lists the last 5 commands you typed.

Which command lets you run a command from history by its number?

A repeat number

B history number

C run number

D !number

Using !number runs the command with that history number.

Describe how to search and reuse a previous command using the Linux history feature.

Think about interactive search and shortcuts to rerun commands.

Explain the purpose and basic usage of the history command in Linux.

Focus on how history helps with command reuse.

Practice

1. What does the history command do in a Linux terminal?

easy

A. Deletes all saved commands

B. Lists all previously executed commands

C. Shows current running processes

D. Clears the terminal screen

Solution

1. Step 1: Understand the purpose of history

   The history command shows a list of commands you typed before in the terminal.

2. Step 2: Compare options with command behavior

   Only Lists all previously executed commands correctly describes this behavior; others describe different commands.

3. Final Answer:

   Lists all previously executed commands -> Option B

4. Quick Check:

   history lists past commands [OK]

Hint: Remember: history shows past commands typed [OK]

Common Mistakes:

• Confusing history with clearing screen
• Thinking history deletes commands
• Mixing history with process listing

2. Which of the following is the correct syntax to rerun the last command starting with git?

easy

A. !!git

B. !$git

C. !git

D. !^git

Solution

1. Step 1: Recall syntax for rerunning commands by prefix

   Using !string reruns the last command starting with string.

2. Step 2: Analyze options

   !git reruns last command starting with 'git'. Others are invalid or incorrect syntax.

3. Final Answer:

   !git -> Option C

4. Quick Check:

   Use !string to rerun commands [OK]

Hint: Use ! plus command start to rerun quickly [OK]

Common Mistakes:

• Using !!git which is invalid
• Confusing !$ with rerun syntax
• Trying !^git which is not correct

3. Given the following history output:

  100  ls -l
  101  git status
  102  cd projects
  103  git commit -m 'fix'

What command will run if you type !git?

medium

A. git commit -m 'fix'

B. git status

C. ls -l

D. cd projects

Solution

1. Step 1: Identify last command starting with 'git'

   From history, commands 101 and 103 start with 'git'. The last one is 103: git commit -m 'fix'.

2. Step 2: Understand !git runs last matching command

   !git reruns the most recent command starting with 'git', which is command 103.

3. Final Answer:

   git commit -m 'fix' -> Option A

4. Quick Check:

   !string runs last command starting with string [OK]

Hint: !string runs last command starting with string [OK]

Common Mistakes:

• Choosing first matching command instead of last
• Confusing command numbers with commands
• Selecting unrelated commands

4. You tried to rerun a command with !cd but got an error: bash: !cd: event not found. What is the likely cause?

medium

A. The shell does not support history

B. You typed the command incorrectly

C. You need to use !! instead

D. No previous command starts with 'cd' in history

Solution

1. Step 1: Understand error meaning

   event not found means no matching command found in history for the given prefix.

2. Step 2: Analyze cause

   If no previous command starts with 'cd', !cd fails with this error.

3. Final Answer:

   No previous command starts with 'cd' in history -> Option D

4. Quick Check:

   !string fails if no matching command [OK]

Hint: Check history for matching commands before using !string [OK]

Common Mistakes:

• Assuming syntax error instead of missing history
• Thinking shell lacks history support
• Using !! instead of !string incorrectly

5. You want to find and rerun a command that contains the word backup anywhere in it, but you don't remember the exact command start. Which is the best way to do this?

hard

A. Press Ctrl + r and type 'backup' to search interactively

B. Use !backup to rerun the command

C. Run history | grep backup and then rerun manually

D. Use !! backup to rerun last backup command

Solution

1. Step 1: Understand searching commands with unknown start

   !string only matches commands starting with string, so !backup won't find commands containing 'backup' elsewhere.

2. Step 2: Identify interactive search method

   Ctrl + r lets you search history interactively for any substring, including 'backup'.

3. Final Answer:

   Press Ctrl + r and type 'backup' to search interactively -> Option A

4. Quick Check:

   Use Ctrl + r for substring history search [OK]

Hint: Use Ctrl + r to search history by any word quickly [OK]

Common Mistakes:

• Assuming !backup matches anywhere in command
• Trying !! backup which is invalid syntax
• Relying only on grep without rerun shortcut