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<title>parse-options API</title>
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<body>
<div id="header">
<h1>parse-options API</h1>
</div>
<div id="preamble">
<div class="sectionbody">
<div class="para"><p>The parse-options API is used to parse and massage options in git
and to provide a usage help with consistent look.</p></div>
</div>
</div>
<h2 id="_basics">Basics</h2>
<div class="sectionbody">
<div class="para"><p>The argument vector <tt>argv[]</tt> may usually contain mandatory or optional
<em>non-option arguments</em>, e.g. a filename or a branch, and <em>options</em>.
Options are optional arguments that start with a dash and
that allow to change the behavior of a command.</p></div>
<div class="ilist"><ul>
<li>
<p>
There are basically three types of options:
<em>boolean</em> options,
options with (mandatory) <em>arguments</em> and
options with <em>optional arguments</em>
(i.e. a boolean option that can be adjusted).
</p>
</li>
<li>
<p>
There are basically two forms of options:
<em>Short options</em> consist of one dash (<tt>-</tt>) and one alphanumeric
character.
<em>Long options</em> begin with two dashes (<tt>--</tt>) and some
alphanumeric characters.
</p>
</li>
<li>
<p>
Options are case-sensitive.
Please define <em>lower-case long options</em> only.
</p>
</li>
</ul></div>
<div class="para"><p>The parse-options API allows:</p></div>
<div class="ilist"><ul>
<li>
<p>
<em>sticked</em> and <em>separate form</em> of options with arguments.
<tt>-oArg</tt> is sticked, <tt>-o Arg</tt> is separate form.
<tt>--option=Arg</tt> is sticked, <tt>--option Arg</tt> is separate form.
</p>
</li>
<li>
<p>
Long options may be <em>abbreviated</em>, as long as the abbreviation
is unambiguous.
</p>
</li>
<li>
<p>
Short options may be bundled, e.g. <tt>-a -b</tt> can be specified as <tt>-ab</tt>.
</p>
</li>
<li>
<p>
Boolean long options can be <em>negated</em> (or <em>unset</em>) by prepending
<tt>no-</tt>, e.g. <tt>--no-abbrev</tt> instead of <tt>--abbrev</tt>.
</p>
</li>
<li>
<p>
Options and non-option arguments can clearly be separated using the <tt>--</tt>
option, e.g. <tt>-a -b --option -- --this-is-a-file</tt> indicates that
<tt>--this-is-a-file</tt> must not be processed as an option.
</p>
</li>
</ul></div>
</div>
<h2 id="_steps_to_parse_options">Steps to parse options</h2>
<div class="sectionbody">
<div class="olist"><ol>
<li>
<p>
<tt>#include "parse-options.h"</tt>
</p>
</li>
<li>
<p>
define a NULL-terminated
<tt>static const char * const builtin_foo_usage[]</tt> array
containing alternative usage strings
</p>
</li>
<li>
<p>
define <tt>builtin_foo_options</tt> array as described below
in section <em>Data Structure</em>.
</p>
</li>
<li>
<p>
in <tt>cmd_foo(int argc, const char **argv, const char *prefix)</tt>
call
</p>
<div class="literalblock">
<div class="content">
<pre><tt>argc = parse_options(argc, argv, prefix, builtin_foo_options, builtin_foo_usage, flags);</tt></pre>
</div></div>
<div class="para"><p><tt>parse_options()</tt> will filter out the processed options of <tt>argv[]</tt> and leave the
non-option arguments in <tt>argv[]</tt>.
<tt>argc</tt> is updated appropriately because of the assignment.</p></div>
<div class="para"><p>You can also pass NULL instead of a usage array as the fifth parameter of
parse_options(), to avoid displaying a help screen with usage info and
option list. This should only be done if necessary, e.g. to implement
a limited parser for only a subset of the options that needs to be run
before the full parser, which in turn shows the full help message.</p></div>
<div class="para"><p>Flags are the bitwise-or of:</p></div>
<div class="vlist"><dl>
<dt>
<tt>PARSE_OPT_KEEP_DASHDASH</tt>
</dt>
<dd>
<p>
Keep the <tt>--</tt> that usually separates options from
non-option arguments.
</p>
</dd>
<dt>
<tt>PARSE_OPT_STOP_AT_NON_OPTION</tt>
</dt>
<dd>
<p>
Usually the whole argument vector is massaged and reordered.
Using this flag, processing is stopped at the first non-option
argument.
</p>
</dd>
<dt>
<tt>PARSE_OPT_KEEP_ARGV0</tt>
</dt>
<dd>
<p>
Keep the first argument, which contains the program name. It's
removed from argv[] by default.
</p>
</dd>
<dt>
<tt>PARSE_OPT_KEEP_UNKNOWN</tt>
</dt>
<dd>
<p>
Keep unknown arguments instead of erroring out. This doesn't
work for all combinations of arguments as users might expect
it to do. E.g. if the first argument in <tt>—unknown —known</tt>
takes a value (which we can't know), the second one is
mistakenly interpreted as a known option. Similarly, if
<tt>PARSE_OPT_STOP_AT_NON_OPTION</tt> is set, the second argument in
<tt>—unknown value</tt> will be mistakenly interpreted as a
non-option, not as a value belonging to the unknown option,
the parser early. That's why parse_options() errors out if
both options are set.
</p>
</dd>
<dt>
<tt>PARSE_OPT_NO_INTERNAL_HELP</tt>
</dt>
<dd>
<p>
By default, parse_options() handles <tt>-h</tt>, <tt>—help</tt> and
<tt>—help-all</tt> internally, by showing a help screen. This option
turns it off and allows one to add custom handlers for these
options, or to just leave them unknown.
</p>
</dd>
</dl></div>
</li>
</ol></div>
</div>
<h2 id="_data_structure">Data Structure</h2>
<div class="sectionbody">
<div class="para"><p>The main data structure is an array of the <tt>option</tt> struct,
say <tt>static struct option builtin_add_options[]</tt>.
There are some macros to easily define options:</p></div>
<div class="vlist"><dl>
<dt>
<tt>OPT__ABBREV(&int_var)</tt>
</dt>
<dd>
<p>
Add <tt>--abbrev[=<n>]</tt>.
</p>
</dd>
<dt>
<tt>OPT__COLOR(&int_var, description)</tt>
</dt>
<dd>
<p>
Add <tt>--color[=<when>]</tt> and <tt>—no-color</tt>.
</p>
</dd>
<dt>
<tt>OPT__DRY_RUN(&int_var)</tt>
</dt>
<dd>
<p>
Add <tt>-n, --dry-run</tt>.
</p>
</dd>
<dt>
<tt>OPT__QUIET(&int_var)</tt>
</dt>
<dd>
<p>
Add <tt>-q, --quiet</tt>.
</p>
</dd>
<dt>
<tt>OPT__VERBOSE(&int_var)</tt>
</dt>
<dd>
<p>
Add <tt>-v, --verbose</tt>.
</p>
</dd>
<dt>
<tt>OPT_GROUP(description)</tt>
</dt>
<dd>
<p>
Start an option group. <tt>description</tt> is a short string that
describes the group or an empty string.
Start the description with an upper-case letter.
</p>
</dd>
<dt>
<tt>OPT_BOOLEAN(short, long, &int_var, description)</tt>
</dt>
<dd>
<p>
Introduce a boolean option.
<tt>int_var</tt> is incremented on each use.
</p>
</dd>
<dt>
<tt>OPT_BIT(short, long, &int_var, description, mask)</tt>
</dt>
<dd>
<p>
Introduce a boolean option.
If used, <tt>int_var</tt> is bitwise-ored with <tt>mask</tt>.
</p>
</dd>
<dt>
<tt>OPT_NEGBIT(short, long, &int_var, description, mask)</tt>
</dt>
<dd>
<p>
Introduce a boolean option.
If used, <tt>int_var</tt> is bitwise-anded with the inverted <tt>mask</tt>.
</p>
</dd>
<dt>
<tt>OPT_SET_INT(short, long, &int_var, description, integer)</tt>
</dt>
<dd>
<p>
Introduce a boolean option.
If used, set <tt>int_var</tt> to <tt>integer</tt>.
</p>
</dd>
<dt>
<tt>OPT_SET_PTR(short, long, &ptr_var, description, ptr)</tt>
</dt>
<dd>
<p>
Introduce a boolean option.
If used, set <tt>ptr_var</tt> to <tt>ptr</tt>.
</p>
</dd>
<dt>
<tt>OPT_STRING(short, long, &str_var, arg_str, description)</tt>
</dt>
<dd>
<p>
Introduce an option with string argument.
The string argument is put into <tt>str_var</tt>.
</p>
</dd>
<dt>
<tt>OPT_INTEGER(short, long, &int_var, description)</tt>
</dt>
<dd>
<p>
Introduce an option with integer argument.
The integer is put into <tt>int_var</tt>.
</p>
</dd>
<dt>
<tt>OPT_DATE(short, long, &int_var, description)</tt>
</dt>
<dd>
<p>
Introduce an option with date argument, see <tt>approxidate()</tt>.
The timestamp is put into <tt>int_var</tt>.
</p>
</dd>
<dt>
<tt>OPT_CALLBACK(short, long, &var, arg_str, description, func_ptr)</tt>
</dt>
<dd>
<p>
Introduce an option with argument.
The argument will be fed into the function given by <tt>func_ptr</tt>
and the result will be put into <tt>var</tt>.
See <em>Option Callbacks</em> below for a more elaborate description.
</p>
</dd>
<dt>
<tt>OPT_FILENAME(short, long, &var, description)</tt>
</dt>
<dd>
<p>
Introduce an option with a filename argument.
The filename will be prefixed by passing the filename along with
the prefix argument of <tt>parse_options()</tt> to <tt>prefix_filename()</tt>.
</p>
</dd>
<dt>
<tt>OPT_ARGUMENT(long, description)</tt>
</dt>
<dd>
<p>
Introduce a long-option argument that will be kept in <tt>argv[]</tt>.
</p>
</dd>
<dt>
<tt>OPT_NUMBER_CALLBACK(&var, description, func_ptr)</tt>
</dt>
<dd>
<p>
Recognize numerical options like -123 and feed the integer as
if it was an argument to the function given by <tt>func_ptr</tt>.
The result will be put into <tt>var</tt>. There can be only one such
option definition. It cannot be negated and it takes no
arguments. Short options that happen to be digits take
precedence over it.
</p>
</dd>
<dt>
<tt>OPT_COLOR_FLAG(short, long, &int_var, description)</tt>
</dt>
<dd>
<p>
Introduce an option that takes an optional argument that can
have one of three values: "always", "never", or "auto". If the
argument is not given, it defaults to "always". The <tt>—no-</tt> form
works like <tt>—long=never</tt>; it cannot take an argument. If
"always", set <tt>int_var</tt> to 1; if "never", set <tt>int_var</tt> to 0; if
"auto", set <tt>int_var</tt> to 1 if stdout is a tty or a pager,
0 otherwise.
</p>
</dd>
</dl></div>
<div class="para"><p>The last element of the array must be <tt>OPT_END()</tt>.</p></div>
<div class="para"><p>If not stated otherwise, interpret the arguments as follows:</p></div>
<div class="ilist"><ul>
<li>
<p>
<tt>short</tt> is a character for the short option
(e.g. <tt>'e'</tt> for <tt>-e</tt>, use <tt>0</tt> to omit),
</p>
</li>
<li>
<p>
<tt>long</tt> is a string for the long option
(e.g. <tt>"example"</tt> for <tt>--example</tt>, use <tt>NULL</tt> to omit),
</p>
</li>
<li>
<p>
<tt>int_var</tt> is an integer variable,
</p>
</li>
<li>
<p>
<tt>str_var</tt> is a string variable (<tt>char *</tt>),
</p>
</li>
<li>
<p>
<tt>arg_str</tt> is the string that is shown as argument
(e.g. <tt>"branch"</tt> will result in <tt><branch></tt>).
If set to <tt>NULL</tt>, three dots (<tt>…</tt>) will be displayed.
</p>
</li>
<li>
<p>
<tt>description</tt> is a short string to describe the effect of the option.
It shall begin with a lower-case letter and a full stop (<tt>.</tt>) shall be
omitted at the end.
</p>
</li>
</ul></div>
</div>
<h2 id="_option_callbacks">Option Callbacks</h2>
<div class="sectionbody">
<div class="para"><p>The function must be defined in this form:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>int func(const struct option *opt, const char *arg, int unset)</tt></pre>
</div></div>
<div class="para"><p>The callback mechanism is as follows:</p></div>
<div class="ilist"><ul>
<li>
<p>
Inside <tt>func</tt>, the only interesting member of the structure
given by <tt>opt</tt> is the void pointer <tt>opt\->value</tt>.
<tt>*opt\->value</tt> will be the value that is saved into <tt>var</tt>, if you
use <tt>OPT_CALLBACK()</tt>.
For example, do <tt>*(unsigned long *)opt\->value = 42;</tt> to get 42
into an <tt>unsigned long</tt> variable.
</p>
</li>
<li>
<p>
Return value <tt>0</tt> indicates success and non-zero return
value will invoke <tt>usage_with_options()</tt> and, thus, die.
</p>
</li>
<li>
<p>
If the user negates the option, <tt>arg</tt> is <tt>NULL</tt> and <tt>unset</tt> is 1.
</p>
</li>
</ul></div>
</div>
<h2 id="_sophisticated_option_parsing">Sophisticated option parsing</h2>
<div class="sectionbody">
<div class="para"><p>If you need, for example, option callbacks with optional arguments
or without arguments at all, or if you need other special cases,
that are not handled by the macros above, you need to specify the
members of the <tt>option</tt> structure manually.</p></div>
<div class="para"><p>This is not covered in this document, but well documented
in <tt>parse-options.h</tt> itself.</p></div>
</div>
<h2 id="_examples">Examples</h2>
<div class="sectionbody">
<div class="para"><p>See <tt>test-parse-options.c</tt> and
<tt>builtin-add.c</tt>,
<tt>builtin-clone.c</tt>,
<tt>builtin-commit.c</tt>,
<tt>builtin-fetch.c</tt>,
<tt>builtin-fsck.c</tt>,
<tt>builtin-rm.c</tt>
for real-world examples.</p></div>
</div>
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Last updated 2010-09-18 23:57:13 UTC
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