hello

Print "Hello, world!"

$ hello

$ hello [[-t|--traditional]]

$ hello [[-g|--greeting]] "[greeting_text]"

hello [-u | --universe]

-u | --universe
    Changes the default greeting from 'Hello, World!' to 'Hello, Universe!'. This option allows for a broader, more generic salutation, suitable for greeting a wider audience or concept.

The hello command is not a standard Linux command. It is typically used as a pedagogical example for a first program or a simple shell script, often encountered in programming tutorials and introductory computer science courses. When created, its primary function is to print a greeting message, most commonly 'Hello, World!', to the standard output. Its exact behavior and available options are entirely dependent on how it is implemented by a user or system administrator, making it a highly customizable but non-universal utility. As it is not part of any standard Linux distribution, users wishing to utilize a 'hello' command must create it themselves, usually as a shell script leveraging core commands like echo or printf to achieve its output.

The hello command is not pre-installed on Linux systems. Its existence and behavior depend entirely on a user-defined implementation. There is no standard manual page (man page) for hello, and its features (options, arguments) can vary widely based on how it was scripted. Users should be aware that running an unknown 'hello' command might execute arbitrary code if it's not a simple greeting script, posing a potential security risk if sourced from untrusted locations.

To create a basic hello command that prints 'Hello, World!' or 'Hello, Universe!', you can create a simple shell script. For example, create a file named hello (without any file extension) in your home directory or a custom bin directory (e.g., ~/bin or ~/.local/bin) with the following content:

#!/bin/bash

# Check if the first argument is -u or --universe
if [ "$1" = "-u" ] || [ "$1" = "--universe" ]; then
  echo "Hello, Universe!"
else
  echo "Hello, World!"
fi

After saving the file, make it executable: chmod +x ~/bin/hello

Finally, ensure the directory containing your script (e.g., ~/bin) is in your system's PATH environment variable for easy execution from any directory. You can add export PATH=$PATH:~/bin to your shell's configuration file (e.g., ~/.bashrc or ~/.zshrc) for persistence.

A user-defined hello command is primarily used as an educational tool for basic scripting, demonstrating concepts like command arguments, conditional logic, and standard output. However, its simplicity makes it highly adaptable. It can be customized to perform a wide array of actions, provide different outputs, interact with files, or even launch other programs, showcasing the fundamental principles of creating custom command-line utilities within a Linux environment.

The concept of a 'hello' program, specifically 'Hello, World!', originates from early programming examples and tutorials. It is widely considered the simplest program that can be written in almost any programming language, demonstrating basic syntax and output functionality. Brian Kernighan's 1978 book 'The C Programming Language' popularized its use. In the context of Linux, while no official 'hello' command exists, it serves as a canonical example for teaching basic shell scripting, file permissions, and the PATH environment variable, representing the 'first steps' in creating one's own command-line utilities. Its ubiquity in learning materials has made it a de facto standard for testing new environments or languages.

echo(1), printf(1), sh(1), bash(1), chmod(1)