Install and Use McFly to Search Bash or ZSH History

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Many Linux users run certain commands regularly. Newcomers might resort to retyping the command or using the up and down keys to scroll through previous commands. More experienced users typically search their terminal history using the built-in Control-r command. The free and open-source McFly application is designed as an alternative to these traditional methods. McFly is a bash search history utility that uses AI techniques to display the most relevant commands. This guide provides a brief introduction to the McFly application and its methodology. It also explains how to install McFly and how to use the mcfly command to search through the terminal history.

An Introduction to McFly

McFly incorporates an AI-based algorithm to bring context and intelligence to its search results rather than relying on a purely linear search. This allows it to preferentially display commands from the terminal history that are more likely to be useful. Although McFly uses a neural network and maintains a SQLite database, it still retrieves results in real-time. Some of the ways McFly prioritizes items from the history log are as follows:

  • It enhances the traditional search history with information about when the command is run and the directory where it is executed. It also keeps track of the exit status of each command, so it can detect failed commands.
  • It considers the current working directory and is more likely to suggest commands that you have run from that directory before.
  • It takes into account the most recent commands and prioritizes commands that have typically followed those commands in the past.
  • It highlights commands that are used regularly, along with recent commands.
  • If a command is selected directly from the McFly interface, it is prioritized in future searches.
  • Commands that resulted in an exit status of Error are less likely to be recommended.

Unlike Control-r, McFly displays its results using a full-screen display, with all available options at the top of the terminal. It also allows users to scrub any command from the database or add additional commands. However, McFly does not replace or overwrite the terminal history maintained by the system. The regular built-in record of the previous commands is still available and can be used at any time. Many users toggle between the two alternatives. McFly is written in the Rust programming language, for extra speed and security, and features full Unicode support. It is available for most systems and can be installed using one of several popular package managers.

The easiest but least efficient method of searching the terminal command history is with the up arrow. This cycles through the most recent commands one by one. This is fairly efficient for running a command that was recently executed but is tedious otherwise. It is also possible to run the history command. This displays all the commands from the terminal’s history, subject to buffer capacity.

A quicker and better way of searching through the terminal history is by using Control-r. This allows users to specify a search term. Commands matching the search are displayed one at a time, starting with the most recent selection. In the example below, when you type Control-r and vi, the most recent command matching the vi string is displayed. In this example, it is vi submenu.json.

(reverse-i-search)`vi': vi submenu.json

If you again enter Control-r, the second-most recent match is displayed. When the user finds the command they are looking for, they have two choices. They can hit the return key to re-run it, or use the left and right arrow keys to edit it before execution.

This works well enough in many cases, but it often forces the user to cycle through multiple iterations before they find the command they want. There is no context or nuance to the search. Control-r begins with the most recent match and works back through the commands in a linear manner, displaying one match at a time. It lacks any of the functionality of McFly. It does not take into account the exit status of the commands, how often the commands were run, or the execution directory of the command. It is also much easier to inadvertently select an unwanted command because Control-r does not use a full-screen interface. McFly is an obvious upgrade over any type of built-in terminal history search on Linux.

Before You Begin

  1. Familiarize yourself with our Getting Started with Linode guide and complete the steps for setting your Linode’s hostname and timezone.

  2. This guide uses sudo wherever possible. Complete the sections of the How to Secure Your Server guide to create a standard user account, harden SSH access and remove unnecessary network services.

  3. Update your system:

     sudo apt-get update && sudo apt-get upgrade
The steps in this guide are written for non-root users. Commands that require elevated privileges are prefixed with sudo. If you are not familiar with the sudo command, see the Linux Users and Groups guide.

How to Install McFly

You can install McFly using the Homebrew package manager or via McFly’s install script.

McFly can also be installed from GitHub or manually from the source. In this case, Rust must also be installed. See the McFly GitHub page for more information.

Install McFly Using Homebrew

The Homebrew package manager installs programs into their own directory and adds all appropriate soft links. To use Homebrew to install McFly, follow the steps below:

  1. Download and install Homebrew using the following command. Enter the sudo password to install Homebrew into its own directory in the /home directory. To install it in your user directory, enter Control-D.

     /bin/bash -c "$(curl -fsSL"
  2. Add Homebrew to the $PATH variable using the following commands. In the first command, substitute your user name for userid.

     echo 'eval "$(/home/linuxbrew/.linuxbrew/bin/brew shellenv)"' >> /home/userid/.profile
     eval "$(/home/linuxbrew/.linuxbrew/bin/brew shellenv)"
  3. (Optional) For added functionality, install the build-essential package.

     sudo apt-get install build-essential
  4. Use the brew command to install the gcc package.

     brew install gcc
  5. To verify Homebrew is installed and working properly, run the brew doctor command.

    Use the brew help command to see a full list of the Homebrew commands.
     brew doctor
    Your system is ready to brew.
  6. Install the Homebrew “tap” for McFly.

     brew tap cantino/mcfly
  7. Install McFly.

     brew install mcfly
  8. Add one of the following lines to the shell configuration file, depending on the shell you are using.

    For a Bash shell, add the following line to ~/.bashrc.

     eval "$(mcfly init bash)"

    For the Zsh shell, add the following line to ~/.zshrc.

     eval "$(mcfly init zsh)"
  9. Source the .bashrc or .zshrc file, depending on the shell you are using.

    For a Bash shell, source the configuration file using the command below:

     source ~/.bashrc

    For a Zsh shell, source the configuration file using the command below:

     source ~/.zshrc
  10. McFly confirms it has imported the history. If the terminal history is very long, you might experience a one-time delay.

    McFly: Importing shell history for the first time. This may take a minute or two...done.

Install McFly Using the Install Script

To download McFly using the installation script, follow the instructions below:

  1. Log in to the system as the root user to avoid problems with permissions.

  2. Use curl to run the install script.

     curl -LSfs | sh -s -- --git cantino/mcfly
  3. Add one of the following lines to the shell configuration file, depending on the shell you are using.

    For a Bash shell, add the following line to ~/.bashrc.

     eval "$(mcfly init bash)"

    For the Zsh shell, add the following line to the .zshrc file.

     eval "$(mcfly init zsh)"
  4. Source the .bashrc or .zshrc file, depending on the shell you are using.

    For a Bash shell, source the configuration file using the command below:

     source ~/.bashrc

    For a Zsh shell, source the configuration file using the command below:

     source ~/.zshrc
  5. McFly confirms it has imported the shell history. If you have a lengthy shell history, you might experience a moderately-long one-time delay.

    McFly: Importing shell history for the first time. This may take a minute or two...done.

Install McFly on macOS

The same methods that is used for Linux systems can also be used on macOS. macOS users can also install McFly using MacPorts. For more information, see the McFly GitHub page.

Configure McFly

McFly uses shell environment variables for configuration. Add the variables shown in the below sections to the shell configuration file, depending on whether you are using ~/.bashrc or ~/.zshrc. When you are done, apply the changes using source ~/.bashrc or source ~/.zshrc.

Change to Light Mode

With the default settings, McFly runs in “Dark Mode”. To change the display to suit for a light terminal, export the MCFLY_LIGHT variable to the shell configuration file.

File: ~/.bashrc

Set the Key Scheme

McFly uses a key scheme based on emacs. For a scheme more similar to vi or vim inspired editors, change the MCFLY_KEY_SCHEME variable.

File: ~/.bashrc

Enable Fuzzy Searching

Fuzzy Searching applies a more lenient search algorithm, where closely related terms are also counted as matches. Some examples might be different tenses of a verb form, plural or collective forms of a noun, and slightly misspelled words. It is also known as Approximate String Matching. To enable fuzzy searching, export the MCFLY_FUZZY variable.

File: ~/.bashrc
export MCFLY_FUZZY=true

Set the Interface View

The McFly interface appears on the top of the screen by default. It can be shifted to the bottom through the use of the MCFLY_INTERFACE_VIEW variable.

File: ~/.bashrc

Set the Number of Results Displayed or Used

McFly allows users to adjust the number of results that are displayed and the depth of the search. The MCFLY_RESULTS variable determines how many results are shown. MCFLY_HISTORY_LIMIT=x limits the depth of the search to the x most recent commands. This variable can increase performance when the McFly database is very large.

File: ~/.bashrc

How to Use McFly

Because it uses an interface, McFly is straightforward to use. There are very few commands to remember. To see more information about all of the options, use the mcfly --help command. The help command explains all of the flags, options, and subcommands.

To use the mcfly command to search the terminal history, follow the steps below.

  1. To run the search, use the command mcfly search <search_term>. The following command searches the McFly database for the term apt.

     mcfly search apt
  2. McFly enters full-screen mode. It displays the possible actions at the top along with a list of all items sorted from most to least relevant. Scroll through the items using the up and down keys.

    Example McFly interface displaying file list

  3. When you have located the relevant entry, hit the return key to run the command. For example, to run the command sudo apt-get update -y && sudo apt-get upgrade -y, select it from the list and then hit the return key.

    Selecting a file using McFly

  4. To edit the command before running it, locate the command following the same procedure as in the previous step. Then select it using the TAB key. This pastes the selected command into the terminal. You can then edit it on the command line like any other command.

  5. To exit the McFly application without running any commands, use the ESC key.

  6. To delete a command from the McFly database, choose the item and type the F2 key. To delete the mcfly search fd command from the list, first select it using the down arrow, then enter F2.

     mcfly search fd

    Deleting a file in McFly

  7. To launch McFly without any search terms, use the mcfly search command without any parameters. You can also use mcfly search "".

     mcfly search

    McFly interface with no starting search term

    You can select an item from the list or start typing to begin a search. McFly updates the results as you type. The display below illustrates how the list is updated after you enter vi.

    Adding text to refine a McFly search

A Demonstration of McFly’s AI Capabilities

McFly displays different results depending on the context of the command and your search history. While it is difficult to predict exactly what commands are displayed, the following examples demonstrate how the results might change.

Once a command is selected from the McFly interface, it is prioritized in future searches. In the earlier example, the command sudo apt-get update -y && sudo apt-get upgrade -y was selected. From now on, it ranks higher in this list when the command mcfly search apt is run. Compare the results of the new search with the earlier results to see the difference.

mcfly search apt

McFly list change with previous search

McFly gives lower priority to commands that result in an error. For example, the command sudo apt instrall nginx results in an error due to the typo in instrall. McFly records the exit status of the command and downgrades it in the results. When mcfly search apt is run again, the command sudo apt instrall nginx is not near the top of the list, even though it occurred recently.

McFly list change with error context

McFly displays different results depending on the directory. In the example below, vi countries.txt is always run from the accounts directory. If a user runs mcfly search vi from the same directory, vi countries.txt appears as one of the top choices.

mcfly search vi

McFly list change in subdirectory

When the user returns to their home directory and runs the same command, vi countries.txt command is no longer at the top of the list. Other commands rank higher even though they were not run recently. This is because the vi countries.txt command is not typically run from the home directory. These results continue to improve as you use McFly because it learns more about when and where different commands are run.

McFly list changes in main directory


McFly is a lightweight open-source utility offering an improved terminal history search compared to typical methods, such as Control-r. It can be installed using a package manager or by using McFly’s own install script. McFly uses a neural network to keep track of when and where each command is run along with its exit status. It prioritizes commands that have been run frequently or have been run from the current working directory before and penalize failed commands.

McFly uses an intuitive full-screen interface. Users can run the mcfly search command to search their bash history for a specific command or display all commands in priority order. From the McFly interface, users can run a command immediately or copy it to the terminal to edit it first. Unwanted commands can be deleted, while several configuration options allow users to customize the application. More information can be found at the McFly GitHub page.

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

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