echo Command ============ The `echo` command is used to output text or data to the shell's standard output, or to a specified destination stream. The data can be provided as parameters to the command, and the command will output that data, followed by a newline by default. Usage ----- The basic syntax for the `echo` command is as follows: .. code-block:: echo Arguments ---------- - `data`: (Required) The text or data to be output to the destination. The data can be any string of characters. Description ----------- The `echo` command takes the input data and writes it to a specified output stream. By default, the data is written to the screen (i.e., the shell’s standard output), but this can be directed to a different stream if specified. This command allows users to display text or data during their shell session, and it can be used for a variety of tasks, such as printing messages, debugging, or generating formatted output. Options ------- - The destination for the output can be changed by specifying a different output stream. If no output stream is specified, the output will be written to the shell's standard output. Examples -------- 1. **Echo text to the screen:** .. code-block:: echo Hello, World! This will output: .. code-block:: Hello, World! 2. **Echo text to a different output stream (e.g., a file):** The command allows specifying a different output stream. If you provide the stream (like a file or a buffer), the command will write the output there instead of the screen. (Assuming support for this stream functionality is implemented elsewhere in the system). Error Handling -------------- If there is an error with the input or output, the following messages will be shown: - **"invalid input to echo command"**: This occurs when no valid data is provided to the command. Notes ----- - The `echo` command automatically appends a newline character (`\n`) after the input data is echoed to the output stream. - The `echo` command can handle strings of arbitrary length. The input data is dynamically allocated in memory. - If no data is supplied, the command will output an error message. - The destination stream can be customized, allowing for flexible usage of the `echo` command in various contexts.