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(libc.info)Example of Getopt

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Example of Parsing Arguments with `getopt'
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   Here is an example showing how `getopt' is typically used.  The key
points to notice are:

   * Normally, `getopt' is called in a loop.  When `getopt' returns
     `-1', indicating no more options are present, the loop terminates.

   * A `switch' statement is used to dispatch on the return value from
     `getopt'.  In typical use, each case just sets a variable that is
     used later in the program.

   * A second loop is used to process the remaining non-option
     arguments.

     #include <unistd.h>
     #include <stdio.h>
     
     int
     main (int argc, char **argv)
     {
       int aflag = 0;
       int bflag = 0;
       char *cvalue = NULL;
       int index;
       int c;
     
       opterr = 0;
     
       while ((c = getopt (argc, argv, "abc:")) != -1)
         switch (c)
           {
           case 'a':
             aflag = 1;
             break;
           case 'b':
             bflag = 1;
             break;
           case 'c':
             cvalue = optarg;
             break;
           case '?':
             if (isprint (optopt))
               fprintf (stderr, "Unknown option `-%c'.\n", optopt);
             else
               fprintf (stderr,
                        "Unknown option character `\\x%x'.\n",
                        optopt);
             return 1;
           default:
             abort ();
           }
     
       printf ("aflag = %d, bflag = %d, cvalue = %s\n",
               aflag, bflag, cvalue);
     
       for (index = optind; index < argc; index++)
         printf ("Non-option argument %s\n", argv[index]);
       return 0;
     }

   Here are some examples showing what this program prints with
different combinations of arguments:

     % testopt
     aflag = 0, bflag = 0, cvalue = (null)
     
     % testopt -a -b
     aflag = 1, bflag = 1, cvalue = (null)
     
     % testopt -ab
     aflag = 1, bflag = 1, cvalue = (null)
     
     % testopt -c foo
     aflag = 0, bflag = 0, cvalue = foo
     
     % testopt -cfoo
     aflag = 0, bflag = 0, cvalue = foo
     
     % testopt arg1
     aflag = 0, bflag = 0, cvalue = (null)
     Non-option argument arg1
     
     % testopt -a arg1
     aflag = 1, bflag = 0, cvalue = (null)
     Non-option argument arg1
     
     % testopt -c foo arg1
     aflag = 0, bflag = 0, cvalue = foo
     Non-option argument arg1
     
     % testopt -a -- -b
     aflag = 1, bflag = 0, cvalue = (null)
     Non-option argument -b
     
     % testopt -a -
     aflag = 1, bflag = 0, cvalue = (null)
     Non-option argument -