In addition, it separates option declarations from usage and help messages becuase the author feels like that's a better idea. 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'). Programming languages C C uses argv to process command-line arguments. 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. It looks something like this: Parses command line arguments argv in order. Over the years, a somewhat standard syntax for command-line arguments has emerged. For example, ARGV[0] returns the first argument passed to the Ruby script. Command-line arguments are just text. When a block is given, each non-option argument is yielded. dup if argv . Let's do a quick overview of the process! Defining the options Start by requiring optparse, and initializing a new OptionParser object with a block that defines which options the parser accepts. Different command-line argument parsing methods are used by different programming languages to parse 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. For dirt-simple argument parsing… 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. 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). Learn how to parse command line options in your Ruby scripts with the OptionParser class, available in the Ruby standard library. 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). size == 1 and Array === argv [ 0 ] parse! # File lib/optparse.rb, line 1441 def parse ( * argv ) argv = argv [ 0 ]. Parsing command-line arguments. The first phase is turning any command-line arguments into a data structure that I can easily consult during the actual program. 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). The usual way So here I am, maintaining the command line arguments, which in turn, will be variables, in four different places. Returns the … Here the 11:12:13 argument of the--time option is passed as argument of the parser.on() block. 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