Parses commandline help options to return vector of valid flag names

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.

cmd_help_parse_flags(help_lines, split_newline = FALSE)

Arguments

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).

Value

character vector of flag names parsed from help text

Details

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.

See also

cmd_help_flags_similar cmd_help_flags_suggest

Examples

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)
}