getopt(3C) — C LIBRARY FUNCTIONS

NAME

getopt − get option letter from argument vector

SYNOPSIS

#include <stdlib.h>
int getopt(int argc, char ∗const ∗argv, const char ∗optstring);
extern char ∗optarg;
extern int optind, opterr;

DESCRIPTION

The function getopt() is a command-line parser. It returns the next option letter in argv that matches a letter in optstring.

The function getopt() places in optind the argv index of the next argument to be processed. The external variable optind is initialized to 1 before the first call to the function getopt().

The argument optstring is a string of recognized option letters; if a letter is followed by a colon, the option is expected to have an argument that may be separated from it by white space.

The variable optarg is set to point to the start of the option argument on return from getopt().

When all options have been processed (i.e., up to the first non-option argument), the function getopt() returns EOF. The special option −− may be used to delimit the end of the options; EOF will be returned and −− will be skipped.

The following rules comprise the System V standard for command-line syntax:

RULE 1: Command names must be between two and nine characters.

RULE 2: Command names must include lower-case letters and digits only.

RULE 3: Option names must be a single character in length.

RULE 4: All options must be delimited by the − character.

RULE 5: Options with no arguments may be grouped behind one delimiter.

RULE 6: The first option-argument following an option may be preceded by white space.

RULE 7: Option arguments cannot be optional.

RULE 8: Groups of option arguments following an option must be separated by commas or separated by white space and quoted.

RULE 9: All options must precede operands on the command line.

RULE 10: The characters −− may be used to delimit the end of the options.

RULE 11: The order of options relative to one another should not matter.

RULE 12: The order of operands may matter and position-related interpretations should be determined on a command-specific basis.

RULE 13: The − character preceded and followed by white space should be used only to mean standard input.

RETURN VALUE

The function getopt() returns a question mark (?) when it encounters an option letter not included in optstring; it also prints an error message on stderr if opterr is set to non-0 (opterr is initialized to 1). The message is printed in the standard error format. getopt() support localized output messages. If the appropriate translated system messages are installed on the system, they are selected by the latest call to setlocale() (using the LC_ALL or LC_MESSAGES categories).

The label defined by a call to setlabel() will be used if available, otherwise the name of the utility (argv[0]) will be used.

EXAMPLE

The following code fragment shows how one might process the options and arguments for a command that takes: mutually exclusive options a and b, exactly one of which is required; an optional option i which takes an option-argument; and at least two arguments.

main(int argc, char ∗argv[] /∗, char envp[]∗/)
/∗ envp is unused in this example ∗/
{
    int             opt, aflg=0, bflg=0, iflg=0, errflg=0, retval ;
    char            ∗cmdname, ∗ifile, ∗ofile ;
    FILE            ∗infile, ∗outfile ;
    extern int      optind, opterr, errno ;
    extern char     ∗optarg ;
     setlabel("UX:example");
    cmdname = argv[0] ;
    opterr = 0 ;    /∗ inhibit getopt err msg ∗/
    while ( (opt=getopt(argc,argv,"abi:")) != EOF ) {
        switch ( opt ) {
        case ’a’ :
            aflg += 1 ; break ;
        case ’b’ :
            bflg += 1 ; break ;
        case ’i’ :
            iflg += 1 ; ifile = optarg ; break ;
        default :   /∗ includes ’?’ case ∗/
            errflg += 1 ; break ;
        }
    }
    if ( errflg>0 || aflg+bflg!=1 || iflg>1 || argc-optind<2 ) {
        usage_err_exit(cmdname) ;
    }
    if ( iflg == 0 ) {
        infile = stdin ;
    } else if ( (infile=fopen(ifile,"r")) == NULL ) {
        open_err_exit(cmdname,ifile,errno) ;
    }
    for ( ; optind<argc ; optind+=1 ) {
        if ( (outfile=fopen(ofile=argv[optind],"r+")) == NULL ) {
            open_err_exit(cmdname,ofile,errno) ;
        }
        if ( (retval=do_work(aflg,bflg,infile,outfile)) != 0 ) {
            work_err_exit(cmdname,ofile,retval) ;
        }
        if ( fclose(outfile) != 0 ) {
            close_err_exit(cmdname,ofile,errno) ;
        }
    }
    exit(0) ;
}

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