7 Syntax of command-line arguments ¶
POSIX recommends these conventions for command-line arguments.
- A command-line argument is an option if it begins with a hyphen
(‘-’).
- Option names are single alphanumeric characters.
- Certain options require an argument.
- An option and its argument may or may not appear as separate tokens.
(In other words, the whitespace separating them is optional).
Thus, -o foo and -ofoo are equivalent.
- One or more options without arguments, followed by at most one option
that takes an argument, may follow a hyphen in a single token.
Thus, -abc is equivalent to -a -b -c.
- Options typically precede other non-option arguments.
- The argument ‘--’ terminates all options; any following arguments
are treated as non-option arguments, even if they begin with a hyphen.
- A token consisting of a single hyphen character is interpreted as an
ordinary non-option argument. By convention, it is used to specify standard
input, standard output, or a file named ‘-’.
GNU adds long options to these conventions:
- A long option consists of two hyphens (‘--’) followed by a name
made of alphanumeric characters and hyphens. Option names are typically one
to three words long, with hyphens to separate words. Abbreviations can be
used for the long option names as long as the abbreviations are unique.
- A long option and its argument may or may not appear as separate
tokens. In the latter case they must be separated by an equal sign ‘=’.
Thus, --foo bar and --foo=bar are equivalent.
The syntax of options with an optional argument is
-<short_option><argument> (without whitespace), or
--<long_option>=<argument>.