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Using History in Linux Command-Line Interface (CLI)

The history functionality in the Linux Command-Line Interface (CLI) allows users to access previously executed commands, providing a convenient way to avoid re-typing the same instructions over and over again. This article aims to delve deep into the concept of command history in the Linux CLI, explaining its various aspects, keystroke combinations, and examples to put it into practice.

Why Is Command History Important?​

  1. Efficiency: Quickly recall and reuse previously executed commands.
  2. Troubleshooting: Review the command history to understand past actions and diagnose issues.
  3. Learning: New users can refer to the history to recall how certain tasks were accomplished.

Mechanisms Behind Command History​

Many Linux shells, like Bash, use the GNU Readline library to handle command history. This library maintains a history list and provides a host of features for interacting with that list.

Keystroke Combinations for Using History​

Here is a table detailing the keystrokes involved in navigating and using the command history in Linux CLI:

KeystrokeDescription
Up ArrowGo to the previous command in history.
Down ArrowGo to the next command in history.
Ctrl + RReverse search through command history.
Ctrl + SForward search through command history (may be disabled on some systems).
Ctrl + PGo to the previous command in history (same as Up Arrow).
Ctrl + NGo to the next command in history (same as Down Arrow).
Ctrl + OExecute the current command found in history and move to the next one.
!!Execute the last command.
!NExecute the N-th command in history.
!-NExecute the command N positions back.
!stringExecute the most recent command that starts with 'string'.
!?string?Execute the most recent command containing 'string'.
Ctrl + UClear the line before the cursor.
Ctrl + KClear the line after the cursor.

Practical Examples​

Let's see how to effectively use the history functionality with some examples. For demonstration purposes, we'll assume you've created a folder named demo_history with some dummy files and folders.

  1. Creating Dummy Files and Directories

    mkdir demo_history
    cd demo_history
    touch file_a.txt file_b.txt

Example 1: Using Up and Down Arrows​

After running a couple of commands, you can press the Up Arrow to cycle backward through your command history and the Down Arrow to cycle forward.

ls[Enter]
cd demo_history[Enter]

Press Up Arrow twice to go back to the ls command.

Press Ctrl + R and start typing a part of a command you've previously run, for instance:

(reverse-i-search)`ls`: ls

Press Enter to execute the found command again.

Example 3: Using !! to Repeat Last Command​

Let's say the last command you ran was:

ls

To rerun this command, simply type !! and press Enter.

Example 4: Using !N to Execute a Specific Command​

You can use the history command to display the list of previously executed commands along with their numbers. To run a specific command number N, you can use !N. For example, to run the 5th command in your history:

!5

Example 5: Using !string to Execute Commands That Start with a String​

If you want to rerun the last command that started with the string "ls", you can use !ls.

!ls

Conclusion​

The history functionality in Linux CLI is a powerful feature that greatly enhances efficiency and productivity. By becoming proficient in navigating and leveraging the command history, you can perform tasks more quickly and accurately, improving your overall experience with the Linux command line.

What Can You Do Next 🙏😊​

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