technical/api-parse-options.html

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 735 <body class="article">
 736 <div id="header">
 737 <h1>parse-options API</h1>
 738 <span id="revdate">2024-04-24</span>
 739 </div>
 740 <div id="content">
 741 <div id="preamble">
 742 <div class="sectionbody">
 743 <div class="paragraph"><p>The parse-options API is used to parse and massage options in Git
 744 and to provide a usage help with consistent look.</p></div>
 745 </div>
 746 </div>
 747 <div class="sect1">
 748 <h2 id="_basics">Basics</h2>
 749 <div class="sectionbody">
 750 <div class="paragraph"><p>The argument vector <code>argv[]</code> may usually contain mandatory or optional
 751 <em>non-option arguments</em>, e.g. a filename or a branch, <em>options</em>, and
 752 <em>subcommands</em>.
 753 Options are optional arguments that start with a dash and
 754 that allow to change the behavior of a command.</p></div>
 755 <div class="ulist"><ul>
 756 <li>
 757 <p>
 758 There are basically three types of options:
 759   <em>boolean</em> options,
 760   options with (mandatory) <em>arguments</em> and
 761   options with <em>optional arguments</em>
 762   (i.e. a boolean option that can be adjusted).
 763 </p>
 764 </li>
 765 <li>
 766 <p>
 767 There are basically two forms of options:
 768   <em>Short options</em> consist of one dash (<code>-</code>) and one alphanumeric
 769   character.
 770   <em>Long options</em> begin with two dashes (<code>--</code>) and some
 771   alphanumeric characters.
 772 </p>
 773 </li>
 774 <li>
 775 <p>
 776 Options are case-sensitive.
 777   Please define <em>lower-case long options</em> only.
 778 </p>
 779 </li>
 780 </ul></div>
 781 <div class="paragraph"><p>The parse-options API allows:</p></div>
 782 <div class="ulist"><ul>
 783 <li>
 784 <p>
 785 <em>stuck</em> and <em>separate form</em> of options with arguments.
 786   <code>-oArg</code> is stuck, <code>-o Arg</code> is separate form.
 787   <code>--option=Arg</code> is stuck, <code>--option Arg</code> is separate form.
 788 </p>
 789 </li>
 790 <li>
 791 <p>
 792 Long options may be <em>abbreviated</em>, as long as the abbreviation
 793   is unambiguous.
 794 </p>
 795 </li>
 796 <li>
 797 <p>
 798 Short options may be bundled, e.g. <code>-a -b</code> can be specified as <code>-ab</code>.
 799 </p>
 800 </li>
 801 <li>
 802 <p>
 803 Boolean long options can be <em>negated</em> (or <em>unset</em>) by prepending
 804   <code>no-</code>, e.g. <code>--no-abbrev</code> instead of <code>--abbrev</code>. Conversely,
 805   options that begin with <code>no-</code> can be <em>negated</em> by removing it.
 806   Other long options can be unset (e.g., set string to NULL, set
 807   integer to 0) by prepending <code>no-</code>.
 808 </p>
 809 </li>
 810 <li>
 811 <p>
 812 Options and non-option arguments can clearly be separated using the <code>--</code>
 813   option, e.g. <code>-a -b --option -- --this-is-a-file</code> indicates that
 814   <code>--this-is-a-file</code> must not be processed as an option.
 815 </p>
 816 </li>
 817 </ul></div>
 818 <div class="paragraph"><p>Subcommands are special in a couple of ways:</p></div>
 819 <div class="ulist"><ul>
 820 <li>
 821 <p>
 822 Subcommands only have long form, and they have no double dash prefix, no
 823   negated form, and no description, and they don&#8217;t take any arguments, and
 824   can&#8217;t be abbreviated.
 825 </p>
 826 </li>
 827 <li>
 828 <p>
 829 There must be exactly one subcommand among the arguments, or zero if the
 830   command has a default operation mode.
 831 </p>
 832 </li>
 833 <li>
 834 <p>
 835 All arguments following the subcommand are considered to be arguments of
 836   the subcommand, and, conversely, arguments meant for the subcommand may
 837   not precede the subcommand.
 838 </p>
 839 </li>
 840 </ul></div>
 841 <div class="paragraph"><p>Therefore, if the options array contains at least one subcommand and
 842 <code>parse_options()</code> encounters the first dashless argument, it will either:</p></div>
 843 <div class="ulist"><ul>
 844 <li>
 845 <p>
 846 stop and return, if that dashless argument is a known subcommand, setting
 847   <code>value</code> to the function pointer associated with that subcommand, storing
 848   the name of the subcommand in argv[0], and leaving the rest of the
 849   arguments unprocessed, or
 850 </p>
 851 </li>
 852 <li>
 853 <p>
 854 stop and return, if it was invoked with the <code>PARSE_OPT_SUBCOMMAND_OPTIONAL</code>
 855   flag and that dashless argument doesn&#8217;t match any subcommands, leaving
 856   <code>value</code> unchanged and the rest of the arguments unprocessed, or
 857 </p>
 858 </li>
 859 <li>
 860 <p>
 861 show error and usage, and abort.
 862 </p>
 863 </li>
 864 </ul></div>
 865 </div>
 866 </div>
 867 <div class="sect1">
 868 <h2 id="_steps_to_parse_options">Steps to parse options</h2>
 869 <div class="sectionbody">
 870 <div class="olist arabic"><ol class="arabic">
 871 <li>
 872 <p>
 873 <code>#include "parse-options.h"</code>
 874 </p>
 875 </li>
 876 <li>
 877 <p>
 878 define a NULL-terminated
 879   <code>static const char * const builtin_foo_usage[]</code> array
 880   containing alternative usage strings
 881 </p>
 882 </li>
 883 <li>
 884 <p>
 885 define <code>builtin_foo_options</code> array as described below
 886   in section <em>Data Structure</em>.
 887 </p>
 888 </li>
 889 <li>
 890 <p>
 891 in <code>cmd_foo(int argc, const char **argv, const char *prefix)</code>
 892   call
 893 </p>
 894 <div class="literalblock">
 895 <div class="content">
 896 <pre><code>argc = parse_options(argc, argv, prefix, builtin_foo_options, builtin_foo_usage, flags);</code></pre>
 897 </div></div>
 898 <div class="paragraph"><p><code>parse_options()</code> will filter out the processed options of <code>argv[]</code> and leave the
 899 non-option arguments in <code>argv[]</code>.
 900 <code>argc</code> is updated appropriately because of the assignment.</p></div>
 901 <div class="paragraph"><p>You can also pass NULL instead of a usage array as the fifth parameter of
 902 parse_options(), to avoid displaying a help screen with usage info and
 903 option list.  This should only be done if necessary, e.g. to implement
 904 a limited parser for only a subset of the options that needs to be run
 905 before the full parser, which in turn shows the full help message.</p></div>
 906 <div class="paragraph"><p>Flags are the bitwise-or of:</p></div>
 907 <div class="dlist"><dl>
 908 <dt class="hdlist1">
 909 <code>PARSE_OPT_KEEP_DASHDASH</code>
 910 </dt>
 911 <dd>
 912 <p>
 913         Keep the <code>--</code> that usually separates options from
 914         non-option arguments.
 915 </p>
 916 </dd>
 917 <dt class="hdlist1">
 918 <code>PARSE_OPT_STOP_AT_NON_OPTION</code>
 919 </dt>
 920 <dd>
 921 <p>
 922         Usually the whole argument vector is massaged and reordered.
 923         Using this flag, processing is stopped at the first non-option
 924         argument.
 925 </p>
 926 </dd>
 927 <dt class="hdlist1">
 928 <code>PARSE_OPT_KEEP_ARGV0</code>
 929 </dt>
 930 <dd>
 931 <p>
 932         Keep the first argument, which contains the program name.  It&#8217;s
 933         removed from argv[] by default.
 934 </p>
 935 </dd>
 936 <dt class="hdlist1">
 937 <code>PARSE_OPT_KEEP_UNKNOWN_OPT</code>
 938 </dt>
 939 <dd>
 940 <p>
 941         Keep unknown options instead of erroring out.  This doesn&#8217;t
 942         work for all combinations of arguments as users might expect
 943         it to do.  E.g. if the first argument in <code>--unknown --known</code>
 944         takes a value (which we can&#8217;t know), the second one is
 945         mistakenly interpreted as a known option.  Similarly, if
 946         <code>PARSE_OPT_STOP_AT_NON_OPTION</code> is set, the second argument in
 947         <code>--unknown value</code> will be mistakenly interpreted as a
 948         non-option, not as a value belonging to the unknown option,
 949         the parser early.  That&#8217;s why parse_options() errors out if
 950         both options are set.
 951         Note that non-option arguments are always kept, even without
 952         this flag.
 953 </p>
 954 </dd>
 955 <dt class="hdlist1">
 956 <code>PARSE_OPT_NO_INTERNAL_HELP</code>
 957 </dt>
 958 <dd>
 959 <p>
 960         By default, parse_options() handles <code>-h</code>, <code>--help</code> and
 961         <code>--help-all</code> internally, by showing a help screen.  This option
 962         turns it off and allows one to add custom handlers for these
 963         options, or to just leave them unknown.
 964 </p>
 965 </dd>
 966 <dt class="hdlist1">
 967 <code>PARSE_OPT_SUBCOMMAND_OPTIONAL</code>
 968 </dt>
 969 <dd>
 970 <p>
 971         Don&#8217;t error out when no subcommand is specified.
 972 </p>
 973 </dd>
 974 </dl></div>
 975 </li>
 976 </ol></div>
 977 <div class="paragraph"><p>Note that <code>PARSE_OPT_STOP_AT_NON_OPTION</code> is incompatible with subcommands;
 978 while <code>PARSE_OPT_KEEP_DASHDASH</code> and <code>PARSE_OPT_KEEP_UNKNOWN_OPT</code> can only be
 979 used with subcommands when combined with <code>PARSE_OPT_SUBCOMMAND_OPTIONAL</code>.</p></div>
 980 </div>
 981 </div>
 982 <div class="sect1">
 983 <h2 id="_data_structure">Data Structure</h2>
 984 <div class="sectionbody">
 985 <div class="paragraph"><p>The main data structure is an array of the <code>option</code> struct,
 986 say <code>static struct option builtin_add_options[]</code>.
 987 There are some macros to easily define options:</p></div>
 988 <div class="dlist"><dl>
 989 <dt class="hdlist1">
 990 <code>OPT__ABBREV(&amp;int_var)</code>
 991 </dt>
 992 <dd>
 993 <p>
 994         Add <code>--abbrev[=&lt;n&gt;]</code>.
 995 </p>
 996 </dd>
 997 <dt class="hdlist1">
 998 <code>OPT__COLOR(&amp;int_var, description)</code>
 999 </dt>
1000 <dd>
1001 <p>
1002         Add <code>--color[=&lt;when&gt;]</code> and <code>--no-color</code>.
1003 </p>
1004 </dd>
1005 <dt class="hdlist1">
1006 <code>OPT__DRY_RUN(&amp;int_var, description)</code>
1007 </dt>
1008 <dd>
1009 <p>
1010         Add <code>-n, --dry-run</code>.
1011 </p>
1012 </dd>
1013 <dt class="hdlist1">
1014 <code>OPT__FORCE(&amp;int_var, description)</code>
1015 </dt>
1016 <dd>
1017 <p>
1018         Add <code>-f, --force</code>.
1019 </p>
1020 </dd>
1021 <dt class="hdlist1">
1022 <code>OPT__QUIET(&amp;int_var, description)</code>
1023 </dt>
1024 <dd>
1025 <p>
1026         Add <code>-q, --quiet</code>.
1027 </p>
1028 </dd>
1029 <dt class="hdlist1">
1030 <code>OPT__VERBOSE(&amp;int_var, description)</code>
1031 </dt>
1032 <dd>
1033 <p>
1034         Add <code>-v, --verbose</code>.
1035 </p>
1036 </dd>
1037 <dt class="hdlist1">
1038 <code>OPT_GROUP(description)</code>
1039 </dt>
1040 <dd>
1041 <p>
1042         Start an option group. <code>description</code> is a short string that
1043         describes the group or an empty string.
1044         Start the description with an upper-case letter.
1045 </p>
1046 </dd>
1047 <dt class="hdlist1">
1048 <code>OPT_BOOL(short, long, &amp;int_var, description)</code>
1049 </dt>
1050 <dd>
1051 <p>
1052         Introduce a boolean option. <code>int_var</code> is set to one with
1053         <code>--option</code> and set to zero with <code>--no-option</code>.
1054 </p>
1055 </dd>
1056 <dt class="hdlist1">
1057 <code>OPT_COUNTUP(short, long, &amp;int_var, description)</code>
1058 </dt>
1059 <dd>
1060 <p>
1061         Introduce a count-up option.
1062         Each use of <code>--option</code> increments <code>int_var</code>, starting from zero
1063         (even if initially negative), and <code>--no-option</code> resets it to
1064         zero. To determine if <code>--option</code> or <code>--no-option</code> was encountered at
1065         all, initialize <code>int_var</code> to a negative value, and if it is still
1066         negative after parse_options(), then neither <code>--option</code> nor
1067         <code>--no-option</code> was seen.
1068 </p>
1069 </dd>
1070 <dt class="hdlist1">
1071 <code>OPT_BIT(short, long, &amp;int_var, description, mask)</code>
1072 </dt>
1073 <dd>
1074 <p>
1075         Introduce a boolean option.
1076         If used, <code>int_var</code> is bitwise-ored with <code>mask</code>.
1077 </p>
1078 </dd>
1079 <dt class="hdlist1">
1080 <code>OPT_NEGBIT(short, long, &amp;int_var, description, mask)</code>
1081 </dt>
1082 <dd>
1083 <p>
1084         Introduce a boolean option.
1085         If used, <code>int_var</code> is bitwise-anded with the inverted <code>mask</code>.
1086 </p>
1087 </dd>
1088 <dt class="hdlist1">
1089 <code>OPT_SET_INT(short, long, &amp;int_var, description, integer)</code>
1090 </dt>
1091 <dd>
1092 <p>
1093         Introduce an integer option.
1094         <code>int_var</code> is set to <code>integer</code> with <code>--option</code>, and
1095         reset to zero with <code>--no-option</code>.
1096 </p>
1097 </dd>
1098 <dt class="hdlist1">
1099 <code>OPT_STRING(short, long, &amp;str_var, arg_str, description)</code>
1100 </dt>
1101 <dd>
1102 <p>
1103         Introduce an option with string argument.
1104         The string argument is put into <code>str_var</code>.
1105 </p>
1106 </dd>
1107 <dt class="hdlist1">
1108 <code>OPT_STRING_LIST(short, long, &amp;struct string_list, arg_str, description)</code>
1109 </dt>
1110 <dd>
1111 <p>
1112         Introduce an option with string argument.
1113         The string argument is stored as an element in <code>string_list</code>.
1114         Use of <code>--no-option</code> will clear the list of preceding values.
1115 </p>
1116 </dd>
1117 <dt class="hdlist1">
1118 <code>OPT_INTEGER(short, long, &amp;int_var, description)</code>
1119 </dt>
1120 <dd>
1121 <p>
1122         Introduce an option with integer argument.
1123         The integer is put into <code>int_var</code>.
1124 </p>
1125 </dd>
1126 <dt class="hdlist1">
1127 <code>OPT_MAGNITUDE(short, long, &amp;unsigned_long_var, description)</code>
1128 </dt>
1129 <dd>
1130 <p>
1131         Introduce an option with a size argument. The argument must be a
1132         non-negative integer and may include a suffix of <em>k</em>, <em>m</em> or <em>g</em> to
1133         scale the provided value by 1024, 1024<sup>2 or 1024</sup>3 respectively.
1134         The scaled value is put into <code>unsigned_long_var</code>.
1135 </p>
1136 </dd>
1137 <dt class="hdlist1">
1138 <code>OPT_EXPIRY_DATE(short, long, &amp;timestamp_t_var, description)</code>
1139 </dt>
1140 <dd>
1141 <p>
1142         Introduce an option with expiry date argument, see <code>parse_expiry_date()</code>.
1143         The timestamp is put into <code>timestamp_t_var</code>.
1144 </p>
1145 </dd>
1146 <dt class="hdlist1">
1147 <code>OPT_CALLBACK(short, long, &amp;var, arg_str, description, func_ptr)</code>
1148 </dt>
1149 <dd>
1150 <p>
1151         Introduce an option with argument.
1152         The argument will be fed into the function given by <code>func_ptr</code>
1153         and the result will be put into <code>var</code>.
1154         See <em>Option Callbacks</em> below for a more elaborate description.
1155 </p>
1156 </dd>
1157 <dt class="hdlist1">
1158 <code>OPT_FILENAME(short, long, &amp;var, description)</code>
1159 </dt>
1160 <dd>
1161 <p>
1162         Introduce an option with a filename argument.
1163         The filename will be prefixed by passing the filename along with
1164         the prefix argument of <code>parse_options()</code> to <code>prefix_filename()</code>.
1165 </p>
1166 </dd>
1167 <dt class="hdlist1">
1168 <code>OPT_NUMBER_CALLBACK(&amp;var, description, func_ptr)</code>
1169 </dt>
1170 <dd>
1171 <p>
1172         Recognize numerical options like -123 and feed the integer as
1173         if it was an argument to the function given by <code>func_ptr</code>.
1174         The result will be put into <code>var</code>.  There can be only one such
1175         option definition.  It cannot be negated and it takes no
1176         arguments.  Short options that happen to be digits take
1177         precedence over it.
1178 </p>
1179 </dd>
1180 <dt class="hdlist1">
1181 <code>OPT_COLOR_FLAG(short, long, &amp;int_var, description)</code>
1182 </dt>
1183 <dd>
1184 <p>
1185         Introduce an option that takes an optional argument that can
1186         have one of three values: "always", "never", or "auto".  If the
1187         argument is not given, it defaults to "always".  The <code>--no-</code> form
1188         works like <code>--long=never</code>; it cannot take an argument.  If
1189         "always", set <code>int_var</code> to 1; if "never", set <code>int_var</code> to 0; if
1190         "auto", set <code>int_var</code> to 1 if stdout is a tty or a pager,
1191         0 otherwise.
1192 </p>
1193 </dd>
1194 <dt class="hdlist1">
1195 <code>OPT_NOOP_NOARG(short, long)</code>
1196 </dt>
1197 <dd>
1198 <p>
1199         Introduce an option that has no effect and takes no arguments.
1200         Use it to hide deprecated options that are still to be recognized
1201         and ignored silently.
1202 </p>
1203 </dd>
1204 <dt class="hdlist1">
1205 <code>OPT_PASSTHRU(short, long, &amp;char_var, arg_str, description, flags)</code>
1206 </dt>
1207 <dd>
1208 <p>
1209         Introduce an option that will be reconstructed into a char* string,
1210         which must be initialized to NULL. This is useful when you need to
1211         pass the command-line option to another command. Any previous value
1212         will be overwritten, so this should only be used for options where
1213         the last one specified on the command line wins.
1214 </p>
1215 </dd>
1216 <dt class="hdlist1">
1217 <code>OPT_PASSTHRU_ARGV(short, long, &amp;strvec_var, arg_str, description, flags)</code>
1218 </dt>
1219 <dd>
1220 <p>
1221         Introduce an option where all instances of it on the command-line will
1222         be reconstructed into a strvec. This is useful when you need to
1223         pass the command-line option, which can be specified multiple times,
1224         to another command.
1225 </p>
1226 </dd>
1227 <dt class="hdlist1">
1228 <code>OPT_CMDMODE(short, long, &amp;int_var, description, enum_val)</code>
1229 </dt>
1230 <dd>
1231 <p>
1232         Define an "operation mode" option, only one of which in the same
1233         group of "operating mode" options that share the same <code>int_var</code>
1234         can be given by the user. <code>int_var</code> is set to <code>enum_val</code> when the
1235         option is used, but an error is reported if other "operating mode"
1236         option has already set its value to the same <code>int_var</code>.
1237         In new commands consider using subcommands instead.
1238 </p>
1239 </dd>
1240 <dt class="hdlist1">
1241 <code>OPT_SUBCOMMAND(long, &amp;fn_ptr, subcommand_fn)</code>
1242 </dt>
1243 <dd>
1244 <p>
1245         Define a subcommand.  <code>subcommand_fn</code> is put into <code>fn_ptr</code> when
1246         this subcommand is used.
1247 </p>
1248 </dd>
1249 </dl></div>
1250 <div class="paragraph"><p>The last element of the array must be <code>OPT_END()</code>.</p></div>
1251 <div class="paragraph"><p>If not stated otherwise, interpret the arguments as follows:</p></div>
1252 <div class="ulist"><ul>
1253 <li>
1254 <p>
1255 <code>short</code> is a character for the short option
1256   (e.g. <code>'e'</code> for <code>-e</code>, use <code>0</code> to omit),
1257 </p>
1258 </li>
1259 <li>
1260 <p>
1261 <code>long</code> is a string for the long option
1262   (e.g. <code>"example"</code> for <code>--example</code>, use <code>NULL</code> to omit),
1263 </p>
1264 </li>
1265 <li>
1266 <p>
1267 <code>int_var</code> is an integer variable,
1268 </p>
1269 </li>
1270 <li>
1271 <p>
1272 <code>str_var</code> is a string variable (<code>char *</code>),
1273 </p>
1274 </li>
1275 <li>
1276 <p>
1277 <code>arg_str</code> is the string that is shown as argument
1278   (e.g. <code>"branch"</code> will result in <code>&lt;branch&gt;</code>).
1279   If set to <code>NULL</code>, three dots (<code>...</code>) will be displayed.
1280 </p>
1281 </li>
1282 <li>
1283 <p>
1284 <code>description</code> is a short string to describe the effect of the option.
1285   It shall begin with a lower-case letter and a full stop (<code>.</code>) shall be
1286   omitted at the end.
1287 </p>
1288 </li>
1289 </ul></div>
1290 </div>
1291 </div>
1292 <div class="sect1">
1293 <h2 id="_option_callbacks">Option Callbacks</h2>
1294 <div class="sectionbody">
1295 <div class="paragraph"><p>The function must be defined in this form:</p></div>
1296 <div class="literalblock">
1297 <div class="content">
1298 <pre><code>int func(const struct option *opt, const char *arg, int unset)</code></pre>
1299 </div></div>
1300 <div class="paragraph"><p>The callback mechanism is as follows:</p></div>
1301 <div class="ulist"><ul>
1302 <li>
1303 <p>
1304 Inside <code>func</code>, the only interesting member of the structure
1305   given by <code>opt</code> is the void pointer <code>opt-&gt;value</code>.
1306   <code>*opt-&gt;value</code> will be the value that is saved into <code>var</code>, if you
1307   use <code>OPT_CALLBACK()</code>.
1308   For example, do <code>*(unsigned long *)opt-&gt;value = 42;</code> to get 42
1309   into an <code>unsigned long</code> variable.
1310 </p>
1311 </li>
1312 <li>
1313 <p>
1314 Return value <code>0</code> indicates success and non-zero return
1315   value will invoke <code>usage_with_options()</code> and, thus, die.
1316 </p>
1317 </li>
1318 <li>
1319 <p>
1320 If the user negates the option, <code>arg</code> is <code>NULL</code> and <code>unset</code> is 1.
1321 </p>
1322 </li>
1323 </ul></div>
1324 </div>
1325 </div>
1326 <div class="sect1">
1327 <h2 id="_sophisticated_option_parsing">Sophisticated option parsing</h2>
1328 <div class="sectionbody">
1329 <div class="paragraph"><p>If you need, for example, option callbacks with optional arguments
1330 or without arguments at all, or if you need other special cases,
1331 that are not handled by the macros above, you need to specify the
1332 members of the <code>option</code> structure manually.</p></div>
1333 <div class="paragraph"><p>This is not covered in this document, but well documented
1334 in <code>parse-options.h</code> itself.</p></div>
1335 </div>
1336 </div>
1337 <div class="sect1">
1338 <h2 id="_examples">Examples</h2>
1339 <div class="sectionbody">
1340 <div class="paragraph"><p>See <code>test-parse-options.c</code> and
1341 <code>builtin/add.c</code>,
1342 <code>builtin/clone.c</code>,
1343 <code>builtin/commit.c</code>,
1344 <code>builtin/fetch.c</code>,
1345 <code>builtin/fsck.c</code>,
1346 <code>builtin/rm.c</code>
1347 for real-world examples.</p></div>
1348 </div>
1349 </div>
1350 </div>
1351 <div id="footnotes"><hr /></div>
1352 <div id="footer">
1353 <div id="footer-text">
1354 Last updated
1355  2022-09-21 15:44:34 PDT
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