How to Use the Command "reflex" (with examples)

Reflex is a tool that watches a directory and reruns a command when certain files change. It is useful for automating tasks during development, such as rebuilding source code, running scripts, or restarting servers. In this article, we will explore different use cases of the “reflex” command with examples.

Use case 1: Rebuild with make if any file changes

Code:

reflex make

Motivation: When working on a project that involves building source code, it can be time-consuming to constantly trigger the build process manually. Reflex eliminates this manual step by automatically rebuilding the project whenever any file changes.

Explanation:

• reflex is the command itself.
• make is the command that will be executed when any file changes.

Example output:

...
Running command: make
...

Use case 2: Compile and run Go application if any .go file changes

Code:

reflex --regex='\go$' go run .

Motivation: When developing a Go application, it can be tedious to manually recompile and rerun the application after making changes. Reflex automates this process by monitoring the directory for changes to any .go file and automatically compiling and running the application.

Explanation:

• reflex is the command itself.
• --regex='\go$' specifies a regular expression to match file changes. In this case, it matches any file ending with .go.
• go run . is the command that will be executed when changes are detected. It compiles and runs the Go application.

Example output:

...
Running command: go run .
...

Use case 3: Ignore a directory when watching for changes

Code:

reflex --inverse-regex='^dir/' command

Motivation: In some cases, there might be directories within the watched directory that we want to exclude from triggering the command. Reflex allows us to specify an inverse regular expression to ignore changes in specific directories.

Explanation:

• reflex is the command itself.
• --inverse-regex='^dir/' specifies a regular expression to ignore changes in directories starting with “dir/”.
• command is the command that will be executed when changes are detected.

Example output:

...
Running command: command
...

Use case 4: Run command when reflex starts and restarts on file changes

Code:

reflex --start-service=true command

Motivation: Sometimes it is necessary to run a command not only when file changes are detected but also when Reflex starts. This can be useful to set up the initial state of a development environment or to start a server.

Explanation:

• reflex is the command itself.
• --start-service=true specifies that the command should be run when Reflex starts and restarts on file changes.
• command is the command that will be executed when changes are detected or when Reflex starts.

Example output:

Running command: command
...
Running command: command
...

Use case 5: Substitute the filename that changed in

Code:

reflex -- echo {}

Motivation: When working with file changes, it can be useful to know which file triggered the command. Reflex allows for customizing the command execution by substituting the filename that changed.

Explanation:

• reflex is the command itself.
• -- is used to separate the Reflex options from the command to execute (echo in this case).
• {} is a placeholder that will be replaced with the filename that changed.

Example output:

file.txt
another-file.txt
...

Conclusion

Reflex is a powerful tool for automating tasks during the development process. By watching a directory and rerunning a command on file changes, it saves time and eliminates the need for manual execution. With the examples provided, you can leverage Reflex to streamline your development workflow and focus on writing code.