pat {arrg} | R Documentation |
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)
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. |
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.
Value
A list capturing the positional arguments, with options in an
attribute. This will not usually be used directly, but passed to arrg()
.
Author(s)
Jon Clayden
See Also
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")