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Last update Wed Jun 18 00:14:33 2008

# std.getopt

Processing of command line options.
The getopt module implements a getopt function, which adheres to the POSIX syntax for command line options. GNU extensions are supported in the form of long options introduced by a double dash ("--"). Support for bundling of command line options, as was the case with the more traditional single-letter approach, is provided but not enabled by default.
Author:
Andrei Alexandrescu
Credits:
This module and its documentation are inspired by Perl's Getopt::Long module. The syntax of D's getopt is simpler than its Perl counterpart because getopt infers the expected parameter types from the static types of the passed-in pointers.

void getopt(T...)(ref string[] args, T opts);
  Synopsis:

      import std.getopt;

      string data = "file.dat";
      int length = 24;
      bool verbose;

      void main(string[] args)
      {
        getopt(
          args,
          "length",  &length,    // numeric
          "file",    &data,      // string
          "verbose", &verbose);  // flag
        ...
      }

  The getopt function takes a reference to the command line (as received by main) as its first argument, and an unbounded number of pairs of strings and pointers. Each string is an option meant to "fill" the value pointed-to by the pointer to its right (the "bound" pointer). The option string in the call to getopt should not start with a dash.
  In all cases, the command-line options that were parsed and used by getopt are removed from args. Whatever in the arguments did not look like an option is left in args for further processing by the program. Values that were unaffected by the options are not touched, so a common idiom is to initialize options to their defaults and then invoke getopt. If a command-line argument is recognized as an option with a parameter and the parameter cannot be parsed properly (e.g. a number is expected but not present), a ConvError exception is thrown.
  Depending on the type of the pointer being bound, getopt recognizes the following kinds of options:
  1. Boolean options. These are the simplest options; all they do is set a Boolean to true:

           bool verbose, debugging;
           getopt(args, "verbose", &verbose, "debug", &debugging);

  2. Numeric options. If an option is bound to a numeric type, a number is expected as the next option, or right within the option separated with an "=" sign:

           uint timeout;
           getopt(args, "timeout", &timeout);

     Invoking the program with "--timeout=5" or "--timeout 5" will set timeout to 5.
  - Incremental options. If an option name has a "+" suffix and is bound to a numeric type, then the option's value tracks the number of times the option occurred on the command line:

          uint paranoid;
          getopt(args, "paranoid+", &paranoid);

    Invoking the program with "--paranoid --paranoid --paranoid" will set paranoid to 3. Note that an incremental option never expects a parameter, e.g. in the command line "--paranoid 42 --paranoid", the "42" does not set paranoid to 42; instead, paranoid is set to 2 and "42" is not considered as part of the program options.
  3. String options. If an option is bound to a string, a string is expected as the next option, or right within the option separated with an "=" sign:

         string outputFile;
         getopt(args, "output", &outputFile);

     Invoking the program with "--output=myfile.txt" or "--output myfile.txt" will set outputFile to "myfile.txt".
  If you want to pass a string containing spaces, you need to use the quoting that is appropriate to your shell, e.g. --output='my file.txt'.
  4. Array options. If an option is bound to an array, a new element is appended to the array each time the option occurs:

         string[] outputFiles;
         getopt(args, "output", &outputFiles);

     Invoking the program with "--output=myfile.txt --output=yourfile.txt" or "--output myfile.txt --output yourfile.txt" will set outputFiles to [ "myfile.txt", "yourfile.txt" ] .
  5. Hash options. If an option is bound to an associative array, a string of the form "name=value" is expected as the next option, or right within the option separated with an "=" sign:

         double[string] tuningParms;
         getopt(args, "tune", &tuningParms);

     Invoking the program with e.g. "--tune=alpha=0.5 --tune beta=0.6" will set tuningParms to [ "alpha" : 0.5, "beta" : 0.6 ].
  In general, keys and values can be of any parsable types.
  6. Delegate options. An option can be bound to a delegate with the signature void delegate(string option) or void delegate(string option, string value).
     - In the void delegate(string option) case, the option string (without the leading dash(es)) is passed to the delegate. After that, the option string is considered handled and removed from the options array.

         void main(string[] args)
         {
           uint verbosityLevel = 1;
           void myHandler(string option)
           {
             if (option == "quiet")
             {
               verbosityLevel = 0;
             }
             else
             {
               assert(option == "verbose");
               verbosityLevel = 2;
             }
           }
           getopt(args, "verbose", &myHandler, "quiet", &myHandler);
         }

     - In the void delegate(string option, string value) case, the option string is handled as an option with one argument, and parsed accordingly. The option and its value are passed to the delegate. After that, whatever was passed to the delegate is considered handled and removed from the list.

         void main(string[] args)
         {
           uint verbosityLevel = 1;
           void myHandler(string option, string value)
           {
             switch (value)
             {
               case "quiet": verbosityLevel = 0; break;
               case "verbose": verbosityLevel = 2; break;
               case "shouting": verbosityLevel = verbosityLevel.max; break;
               default :
                 writeln(stderr, "Dunno how verbose you want me to be by saying ",
                   value);
                 exit(1);
             }
           }
           getopt(args, "verbosity", &myHandler);
         }

  Options with multiple names
  Sometimes option synonyms are desirable, e.g. "--verbose", "--loquacious", and "--garrulous" should have the same effect. Such alternate option names can be included in the option specification, using "|" as a separator:

      bool verbose;
      getopt(args, "verbose|loquacious|garrulous", &verbose);

  Case
  By default options are case-insensitive. You can change that behavior by passing getopt the caseSensitive directive like this:

      bool foo, bar;
      getopt(args,
          std.getopt.config.caseSensitive,
          "foo", &foo,
          "bar", &bar);

  In the example above, "--foo", "--bar", "--FOo", "--bAr" etc. are recognized. The directive is active til the end of getopt, or until the converse directive caseInsensitive is encountered:

      bool foo, bar;
      getopt(args,
          std.getopt.config.caseSensitive,
          "foo", &foo,
          std.getopt.config.caseInsensitive,
          "bar", &bar);

  The option "--Foo" is rejected due to std.getopt.config.caseSensitive, but not "--Bar", "--bAr" etc. because the directive std.getopt.config.caseInsensitive turned sensitivity off before option "bar" was parsed.
  Bundling
  Single-letter options can be bundled together, i.e. "-abc" is the same as "-a -b -c". By default, this confusing option is turned off. You can turn it on with the std.getopt.config.bundling directive:

      bool foo, bar;
      getopt(args,
          std.getopt.config.bundling,
          "foo|f", &foo,
          "bar|b", &bar);

  In case you want to only enable bundling for some of the parameters, bundling can be turned off with std.getopt.config.noBundling.
  Passing unrecognized options through
  If an application needs to do its own processing of whichever arguments getopt did not understand, it can pass the std.getopt.config.passThrough directive to getopt:

      bool foo, bar;
      getopt(args,
          std.getopt.config.passThrough,
          "foo", &foo,
          "bar", &bar);

  An unrecognized option such as "--baz" will be found untouched in args after getopt returns.
  Options Terminator
  A lonesome double-dash terminates getopt gathering. It is used to separate program options from other parameters (e.g. options to be passed to another program). Invoking the example above with "--foo -- --bar" parses foo but leaves "--bar" in args. The double-dash itself is removed from the argument array.
enum config;
  Configuration options for getopt. You can pass them to getopt in any position, except in between an option string and its bound pointer.
  caseSensitive
    Turns case sensitivity on
  caseInsensitive
    Turns case sensitivity off
  bundling
    Turns bundling on
  noBundling
    Turns bundling off
  passThrough
    Pass unrecognized arguments through
  noPassThrough
    Signal unrecognized arguments as errors
  stopOnFirstNonOption
    Stop at first argument that does not look like an option

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