cmd_help_parse_flags: Parses commandline help options to return vector of valid...
In snystrom/dotargs: Framework for Building Interfaces to Shell Commands

Description Usage Arguments Details Value See Also Examples

When using cmdfun to write lazy shell wrappers, the user can easily mistype a commandline flag since there is not text completion. Some programs behave unexpectedly when flags are typed incorrectly, and for this reason return uninformative error messages.

1	cmd_help_parse_flags(help_lines, split_newline = FALSE)

`help_lines`	`character` vector containing the output of "command –help", or similar output. Optional: pass either `stdout`, or `stderr` output from processx::run(), must set `processx = TRUE`.
`split_newline`	`logical(1)` if set to TRUE will split string on "\n" before parsing (useful when parsing output from `processx`).

cmd_help_parse_flags tries to grab flags from –help documentation which can be used for error checking. It will try to parse flags following "-" or "–" while ignoring hyphenated words in help text. Although this should cover most use-cases, it may be necessary to write a custom help-text parser for nonstandard tools. Inspect this output carefully before proceeding. Most often, characters are leftover at the end of parsed names, which will require additional parsing.

character vector of flag names parsed from help text

cmd_help_flags_similar cmd_help_flags_suggest

if (.Platform$OS.type == "unix" & file.exists("/bin/tar")) {
# below are two examples parsing the --help method of GNU tar 

# with processx
if (require(processx)) {
out <- processx::run("tar", "--help", error_on_status = FALSE)
fn_flags <- cmd_help_parse_flags(out$stdout, split_newline = TRUE)
}

# with system2
lines <- system2("tar", "--help", stderr = TRUE)
fn_flags <- cmd_help_parse_flags(lines)

# NOTE: some of the "tar" flags contain the extra characters: "\[", "\)", and ";"
# ie "one-top-level\[" which should be "one-top-level"
# These can be additionally parsed using
gsub("[\\[;\\)]", "", fn_flags)
}