POSIX recommends these conventions for command line arguments.
getopt (see section Parsing Program Options) makes it easy to implement them.
isalnum; see section Classification of Characters).
ldcommand requires an argument--an output file name.
getoptin the GNU C library normally makes it appear as if all the option arguments were specified before all the non-option arguments for the purposes of parsing, even if the user of your program intermixed option and non-option arguments. It does this by reordering the elements of the argv array. This behavior is nonstandard; if you want to suppress it, define the
_POSIX_OPTION_ORDERenvironment variable. See section Standard Environment Variables.
GNU adds long options to these conventions. Long options consist of `--' followed by a name made of alphanumeric characters and dashes. Option names are typically one to three words long, with hyphens to separate words. Users can abbreviate the option names as long as the abbreviations are unique.
To specify an argument for a long option, write `--name=value'. This syntax enables a long option to accept an argument that is itself optional.
Eventually, the GNU system will provide completion for long option names in the shell.
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