arrg (version 0.1.0)

pat: Specify a usage pattern

Description

This function is used to specify a valid usage pattern for the command, which may be one of a number of mutually exclusive patterns available. Its return value is generally passed to arrg().

Usage

pat(..., options = NULL)

Value

A list capturing the positional arguments, with options in an attribute. This will not usually be used directly, but passed to arrg().

Arguments

...

Character strings naming positional arguments, if any are valid. Positional arguments are required by default; if not required they should be followed by a question mark. The final positional argument (only) may take multiple values, in which case it should contain an ellipsis (...), before the question mark if the argument is also optional.

options

A string naming the long or short labels of options that can be specified with this pattern, comma-separated. Short form options may be given in one letter cluster for convenience. Options are only required if followed by an exclamation mark.

Author

Jon Clayden

Details

When parsing arguments, patterns are tried in the order specified, and the first valid pattern will be chosen. A pattern will be considered a valid match if all required options and positional arguments have been specified, and no unexpected options are included.

See Also

arrg()

Examples

  # A pattern with no positional arguments, but requiring the -h flag
  pat(options="h!")
  
  # A pattern that takes a command and variable number of arguments, and
  # accepts the -n and -t options (note the latter are specified in cluster
  # form, but "n,t" is also valid) 
  pat("command", "arg...?", options="nt")