The “erl” command is a utility used to run and manage programs written in the Erlang programming language. Erlang is a powerful and concurrent functional programming language that is widely used for building scalable and fault-tolerant systems. The “erl” command provides an interactive environment and various options to execute Erlang programs and manage Erlang-related tasks.
Here’s a more detailed explanation of the “erl” command and its key features:
- Interactive Shell: When executed without any arguments, the “erl” command launches an interactive shell known as the Erlang shell or Erlang REPL (Read-Eval-Print Loop). The shell provides a command-line interface where you can enter and execute Erlang code interactively, making it convenient for testing and experimenting with Erlang programs.
- Program Execution: The “erl” command allows you to execute Erlang programs stored in files. You can pass the name of the file as an argument, and the “erl” command will execute the code within the file and display the output or error messages, if any.
- Erlang Virtual Machine: When you run the “erl” command, it starts the Erlang Virtual Machine (BEAM), which is responsible for executing Erlang code. The Erlang VM provides features like process management, memory management, garbage collection, and concurrency control, which are fundamental to the scalability and reliability of Erlang applications.
- Module Loading and Compilation: The “erl” command supports module loading and compilation. Erlang programs are typically organized into modules, and the “erl” command can load and compile these modules on-demand. This allows you to use functions and data structures defined in other modules and libraries within your Erlang program.
- System Administration: The “erl” command provides options for system administration tasks, such as starting and stopping Erlang nodes (distributed Erlang instances), connecting to remote nodes, monitoring and inspecting running processes, managing clusters, and more. These features facilitate the management and monitoring of Erlang-based distributed systems.
- Command-Line Options: The “erl” command supports various command-line options that allow you to customize the behavior of the Erlang runtime. These options include specifying the Erlang node name, setting the node type (e.g., interactive or daemon), configuring distributed communication, enabling debugging features, controlling memory allocation, and more.
- Integration with Development Tools: Erlang has a rich ecosystem of development tools, and the “erl” command integrates with these tools seamlessly. For example, you can use the “erl” command in conjunction with the Erlang compiler (“erlc”) to compile Erlang source files into bytecode, and then execute the resulting BEAM files using the “erl” command.
- Erlang Libraries and Frameworks: The “erl” command allows you to leverage the extensive standard library and various frameworks available in the Erlang ecosystem. These libraries provide a wide range of functionalities, including network communication, distributed computing, fault tolerance, database access, web development, and more.
The “erl” command is a versatile tool that enables you to run and manage programs written in Erlang. Whether you need to execute Erlang code interactively, run standalone Erlang programs, perform system administration tasks, or leverage the Erlang ecosystem, the “erl” command provides the necessary environment and tools to work with Erlang effectively.
erl Command Examples
1. Compile and run sequential Erlang program as a common script and then exit:
# erlc files && erl -noshell 'mymodule:myfunction(arguments), init:stop().'
2. Connect to a running Erlang node:
# erl -remsh nodename@hostname -sname custom_shortname -hidden -setcookie cookie_of_remote_node
3. Tell the Erlang shell to load modules from a directory:
# erl -pa directory_with_beam_files