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| <h4 class="subsection">25.1.1 Program Argument Syntax Conventions</h4> |
| |
| <p><a name="index-program-argument-syntax-3016"></a><a name="index-syntax_002c-for-program-arguments-3017"></a><a name="index-command-argument-syntax-3018"></a> |
| POSIX recommends these conventions for command line arguments. |
| <code>getopt</code> (see <a href="Getopt.html#Getopt">Getopt</a>) and <code>argp_parse</code> (see <a href="Argp.html#Argp">Argp</a>) make |
| it easy to implement them. |
| |
| <ul> |
| <li>Arguments are options if they begin with a hyphen delimiter (‘<samp><span class="samp">-</span></samp>’). |
| |
| <li>Multiple options may follow a hyphen delimiter in a single token if |
| the options do not take arguments. Thus, ‘<samp><span class="samp">-abc</span></samp>’ is equivalent to |
| ‘<samp><span class="samp">-a -b -c</span></samp>’. |
| |
| <li>Option names are single alphanumeric characters (as for <code>isalnum</code>; |
| see <a href="Classification-of-Characters.html#Classification-of-Characters">Classification of Characters</a>). |
| |
| <li>Certain options require an argument. For example, the ‘<samp><span class="samp">-o</span></samp>’ command |
| of the <code>ld</code> command requires an argument—an output file name. |
| |
| <li>An option and its argument may or may not appear as separate tokens. (In |
| other words, the whitespace separating them is optional.) Thus, |
| ‘<samp><span class="samp">-o foo</span></samp>’<!-- /@w --> and ‘<samp><span class="samp">-ofoo</span></samp>’ are equivalent. |
| |
| <li>Options typically precede other non-option arguments. |
| |
| <p>The implementations of <code>getopt</code> and <code>argp_parse</code> in the GNU C |
| library normally make 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. They do this by reordering the elements of the |
| <var>argv</var> array. This behavior is nonstandard; if you want to suppress |
| it, define the <code>_POSIX_OPTION_ORDER</code> environment variable. |
| See <a href="Standard-Environment.html#Standard-Environment">Standard Environment</a>. |
| |
| <li>The argument ‘<samp><span class="samp">--</span></samp>’ terminates all options; any following arguments |
| are treated as non-option arguments, even if they begin with a hyphen. |
| |
| <li>A token consisting of a single hyphen character is interpreted as an |
| ordinary non-option argument. By convention, it is used to specify |
| input from or output to the standard input and output streams. |
| |
| <li>Options may be supplied in any order, or appear multiple times. The |
| interpretation is left up to the particular application program. |
| </ul> |
| |
| <p><a name="index-long_002dnamed-options-3019"></a>GNU adds <dfn>long options</dfn> to these conventions. Long options consist |
| of ‘<samp><span class="samp">--</span></samp>’ 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. |
| |
| <p>To specify an argument for a long option, write |
| ‘<samp><span class="samp">--</span><var>name</var><span class="samp">=</span><var>value</var></samp>’. This syntax enables a long option to |
| accept an argument that is itself optional. |
| |
| <p>Eventually, the GNU system will provide completion for long option names |
| in the shell. |
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