For example, ARGV[0] returns the first argument passed to the Ruby script. Every time I need to write a Bash script which accepts command line arguments, I go back to this great answer in StackOverflow - How do I parse command line arguments in Bash. Different command-line argument parsing methods are used by different programming languages to parse command-line arguments. The usual way So here I am, maintaining the command line arguments, which in turn, will be variables, in four different places. size == 1 and Array === argv [ 0 ] parse! Here, Ill use OptionParser to write cat2.rb, a second Ruby version of cat that supports a few of the real cats command-line arguments. Programming languages C C uses argv to process command-line arguments. Also, the time argument is nil if no argument is provided to the--time option. It looks something like this: Passing in arguments via the command line is an extremely basic programming task, and a necessity for anyone trying to write a simple Command-Line Interface (CLI). The Ruby options are terminated by the first word on the command line that doesn't start with a hyphen, or by the special flag ``--'' (two hyphens). If no filename is present on the command line, or if the filename is a single hyphen (-), Ruby reads the program source from standard input.Arguments for the program itself follow the program name. ARGV is a built-in array in Ruby for parsing command line arguments. Clint is an alternative Ruby command line argument parser that's very good for programs using the subcommand pattern familiar from git(1), svn(1), apt-get(8), and many others. When optional into keyword argument is provided, the parsed option values are stored there via []= method (so it can be Hash, or OpenStruct, or other similar object). In Node.js, as in C and many related environments, all command-line arguments received by the shell are given to the process in an array called argv (short for 'argument values'). Over the years, a somewhat standard syntax for command-line arguments has emerged. Command-line arguments are just text. Let's do a quick overview of the process! The first phase is turning any command-line arguments into a data structure that I can easily consult during the actual program. When a block is given, each non-option argument is yielded. dup if argv . Parses command line arguments argv in order when environment variable POSIXLY_CORRECT is set, and in permutation mode otherwise. Here the 11:12:13 argument of the--time option is passed as argument of the parser.on() block. If you want the text to mean anything, you're going to have to parse it. Fortunately, there are several good libraries that can help you with the parsing. 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