The history command brings previously used commands forward to use again. So what could be a more appropriate name for a history replacement than the last name of Michael J. Fox's character in Back to the Future? McFly [1] replaces history with an improved interface and more contextualized results that are generated with an AI-based algorithm and an SQLite database. Although no quicker with results than history, McFly offers numerous advantages:

• Results are displayed full-screen, with basic commands summarized in the titlebar (Figure 1).

Figure 1: Unlike history, McFly uses a result screen, with a summary of navigation keys in the titlebar.

• Information is given about when a result was run and in which directory, if it was not in your home directory, as well as if it failed. Failed results are usually not displayed.
• Priority is given to the present working directory.
• Results take into account other commands that in the past were run after the command.

Unlike the history command (Figure 2), McFly does not number results, so you can cannot jump to a specific one. However, numbering is rarely useful, and McFly's contextualized results, as well as the ability to launch a command from the results page, more than compensate for the lack of numbering. Similarly, the ability to edit a result in McFly means that history's complicated editing tools are unnecessary. In addition, McFly's structure is easier to use than history's, which many users ignore when searching history in favor of the up and down arrow keys.

Figure 2: Search results with the old history command.

Installing and Configuring McFly

McFly runs on the Bash and Zsh command shells, with support for the fish shell in development. McFly can be installed using Homebrew [2] or using its installation script. To use the installation script as shown in Figure 3, run the following with root privileges:

curl -LSfs https://raw.githubusercontent.com/cantino/mcfly/master/ci/install.sh | sh -s -- --git cantino/mcfly

Figure 3: McFly's installation script starting up.

Then add the following line to the ~/.bashrc file

eval "$(mcfly init bash)"

or to ~.zshrc

eval "$(mcfly init zsh)"

Finally, to link McFly to the shell, run

source ~/.bashrc

or

source ~/.zshrc

In both cases, finish by importing the shell history (Figure 4). On older or much-used machines, the process may take several minutes.

Figure 4: The first time it runs, McFly imports history's list of commands.

At this point, McFly is ready to run, but you may want to configure it in ~/.bashrc or ~/.zshrc with the options shown in Table 1.

Running McFly

McFly's basic syntax for searching is simple:

McFly search STRING

The basic navigation appears in the titlebar of the results page (see Table 2).

You can also display McFly's complete history and scroll through it with the up and down arrow keys. Using the arrow keys is usually the least effective way to use McFly, but it is probably the most common way to access history when you are using the same command several times in a row. Providing this functionality makes McFly a complete replacement for history.

Results may change depending on the directory from which McFly is run, which can return more accurate results, but can also confuse users or complicate results. Similarly, if results are set to display in priority, a previously selected command is given priority, while a command that results in an error is not displayed or given lower priority. As you continue to use McFly, the results should improve as McFly adjusts to your use of commands. The search sub-command can take the option --fuzzy (-f) NUMBER for a fuzzy search and --results (-r) NUMBER to specify the maximum number of results. In addition, --output-selection (-o) PATH saves the results to a file.

Many users may only use the search sub-command. However, McFly also supports other sub-commands, although they are not documented by any man page, only by brief entries accessed from the --help SUB-COMMAND option. The add sub-command can add to the history, using --dir (-d) to specify where the command was run, --exit (-e) EXIT-CODE to specify an exit code, and --when (-w) to set when the command was run. Similarly, move can specify an old directory (OLD_DIR_PATH) and a new one (NEW_DIR_PATH) in that order. The sub-commands init and train are also available for developers, but appear to be undocumented. However, the other sub-commands can be used by users to assist McFly in improving its search results.

Is McFly Worth Using?

At least initially, algorithms that can be trained must be taken on faith. All I can say with confidence is that several weeks of semi-regular use did not noticeably improve McFly's results. However, such limited, inconsistent trials are inconclusive. It seems likely that heavier use or a longer trial period would produce clearer results. Documentation on how to use the train sub-command would probably be useful as well.

However, even without a learning algorithm, McFly has decided benefits over history. Not only is McFly customizable, both through its environmental variables and the add and move sub-commands, but its simple interface makes it much easier to use than history. Even with the verdict still out about its learning capabilities, McFly's design makes it one of the new breed of modern Linux commands that are replacing so many of the venerable ones.