subgetopt 3 user commands djbwares
subgetopt get option character from command line

    .B #include <subgetopt.h>

    char *\fBsgoptarg\fP;
    .br
    int \fBsgoptind\fP;
    .br
    int \fBsgoptpos\fP;
    .br
    int \fBsgoptdone\fP;
    .br
    int \fBsgoptproblem\fP;

    int \fBsgopt(\fP\fIargc,argv,opts\fR\fB)\fP;

    int \fIargc\fR;
    .br
    char **\fIargv\fR;
    .br
    char *\fIopts\fR;

## Description

.B sgopt returns the next valid command-line option character from .IR argv . Valid option characters are listed in the .I opts string. .I opts may be empty. A character in .I opts may be followed by a colon, in which case it takes an .I option argument\fR. Avoid using the characters ?, :, and \- as option characters. Below .I option argument is abbreviated as .I optarg and .I command-line argument is abbreviated as .IR cmdarg . Options are listed in cmdargs which begin with a minus sign. Several options which do not take optargs may be combined into one cmdarg. An option which takes an optarg may be handled in two ways. If it appears at the very end of a cmdarg, then the entire next cmdarg is the optarg. But if there are any characters in the cmdarg after the option character, then those characters form the optarg. The optarg is returned in .BR sgoptarg . Next time .B sgopt looks at the cmdarg which follows the optarg. If a cmdarg does not begin with a hyphen, or if it is a lone hyphen not followed by any characters, or if it begins with two hyphens, then it terminates option processing, and .B sgopt returns an appropriate code. If there are two hyphens, .B sgopt will advance attention to the next cmdarg, so it can be called again to read further options. .SH "PROPER USAGE" .B sgoptproblem should be used only when .B sgopt returns ?. .B sgoptind and .B sgoptpos are defined all the time. .B sgoptarg is defined all the time; it is null unless .B sgopt has just returned an option with optarg. .B sgopt is typically used as follows.

    #include <subgetopt.h>

    main(argc,argv) int argc; char **argv; { int opt;

    while ((opt = sgopt(argc,argv,"a:s")) != sgoptdone)
    .br
      switch(opt) {
    .br
        case 'a':
    .br
          printf("opt a with optarg %s\\n",sgoptarg); break;
    .br
        case 's':
    .br
          printf("opt s with no optarg\\n"); break;
    .br
        case '?':
    .br
          if (argv[sgoptind] && (sgoptind < argc))
    .br
            printf("illegal opt %c\\n",sgoptproblem);
    .br
          else
    .br
            printf("missing arg, opt %c\\n",sgoptproblem);
    .br
          exit(1);
    .br
      }

    argv += sgoptind;
    .br
    while (*argv) printf("argument %s\\n",*argv++);
    .br
    exit(0);
    .br
    }

The end of the command line is marked by either .IR argc , or a null pointer in .IR argv , whichever comes first. Normally these two markers coincide, so it is redundant to test for both .I argv\fB[sgoptind] and .B sgoptind < \fIargc\fR. The above code shows both tests as an illustration. .B Multiple option sets: One useful technique is to call .B sgopt with a primary .I opts until it returns EOF, then call .B sgopt with a secondary .I opts until it returns EOF. The user can provide primary options, then a double hyphen, and then secondary options. No special handling is needed if some or all of the options are omitted. The same technique can be used for any number of option sets in series. .B Multiple command lines: Before parsing a new .BR argv , make sure to set .B sgoptind and .B sgoptpos back to 1 and 0. .SH "PARSING STAGES" .B sgopt keeps track of its position in .I argv with .B sgoptind and .BR sgoptpos , which are initialized to 1 and 0. It looks at .I argv\fB[sgoptind][sgoptpos] and following characters. .B sgopt indicates that no more options are available by returning .BR sgoptdone , which is initialized to .BR SUBGETOPTDONE , which is defined as \-1. .B sgopt begins by setting .B optarg to null. .B Ending conditions: If .I argv is null, or .B sgoptind is larger than .IR argc , or the current cmdarg .I argv\fB[sgoptind] is null, then .B sgopt returns .BR optdone . .B Stage one: If the current character is zero, .B sgopt moves to the beginning of the next cmdarg. It then checks the ending conditions again. .B Stage two: If the current position is the begining of the cmdarg, .B sgopt checks whether the current character is a minus sign. If not it returns .BR optdone . It then moves to the next character. If that character is zero, .B sgopt moves back to the beginning of the cmdarg, and returns .BR sgoptdone . If the character is a minus sign, .B sgopt moves to the beginning of the next cmdarg, and returns .BR sgoptdone . .B Stage three: .B sgopt records the current character, .IR c , and moves to the next character. There are three possibilities: (1) .I c is an option character without optarg in .IR opts , or (2) .I c is an option character with optarg in .IR opts , or (3) .I c does not appear in .IR opts . (1) If .I c appears as an option character without optarg in .IR opts , .B sgopt returns .IR c . (2) If .I c appears as an option character with optarg in .IR opts , .B sgopt sets .B sgoptarg to the current position, and moves to the next cmdarg. If .B sgoptarg is nonempty, .B sgopt returns .IR c . Then .B sgopt sets .B sgoptarg to the current cmdarg. If the current cmdarg is null, or past .IR argc , .B sgopt sets .B sgoptproblem to .I c and returns ?. Otherwise .B sgopt moves to the next argument and returns .IR c . (2) If .I c does not appear in .IR opts , .B sgopt sets .B sgoptproblem to .I c and returns ?. .SH "SYNTAX NOTE" .B sgopt is actually a macro abbreviation for .BR subgetopt . The external .B sg variables are also macros for .BR subget . These macros are defined in .BR <subgetopt.h> , unless .B SUBGETOPTNOSHORT is defined when .B <subgetopt.h> is included. .SH VERSION subgetopt version 0.9, 931129.

## Author

Original code and documentation by Daniel J. Bernstein, who placed it into the public domain. Converted to DocBook XML by Jonathan de Boyne Pollard.