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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.

License:
Boost License 1.0.

Authors:
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.

Source:
std/getopt.d

void getopt(T...)(ref string[] args, T opts);
Parse and remove command line options from an string array.

Synopsis:
import std.getopt;

string data = "file.dat";
int length = 24;
bool verbose;
enum Color { no, yes };
Color color;

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

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 Exception exception is thrown.

Depending on the type of the pointer being bound, getopt recognizes the following kinds of options:

  1. Boolean options. A lone argument sets the option to true. Additionally true or false can be set within the option separated with an "=" sign:

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

    To set verbose to true, invoke the program with either --verbose or --verbose=true.

    To set debugging to false, invoke the program with --debugging=false.

  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);
    

    To set timeout to 5, invoke the program with either --timeout=5 or --timeout 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 normal program arguments.
  3. Enum options. If an option is bound to an enum, an enum symbol as a string is expected as the next option, or right within the option separated with an "=" sign:

      enum Color { no, yes };
      Color color; // default initialized to Color.no
      getopt(args, "color", &color);
    

    To set color to Color.yes, invoke the program with either --color=yes or --color yes.
  4. 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'.
  5. 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" ] .
  6. 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.
  7. Callback options. An option can be bound to a function or delegate with the signature void function(), void function(string option), void function(string option, string value), or their delegate equivalents.

    • If the callback doesn't take any arguments, the callback is invoked whenever the option is seen.
    • If the callback takes one string argument, the option string (without the leading dash(es)) is passed to the callback. 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);
      }
      

    • If the callback takes two string arguments, the option string is handled as an option with one argument, and parsed accordingly. The option and its value are passed to the callback. After that, whatever was passed to the callback 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 :
              stderr.writeln("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.

"Short" versus "long" options

Traditionally, programs accepted single-letter options preceded by only one dash (e.g. -t). getopt accepts such parameters seamlessly. When used with a double-dash (e.g. --t), a single-letter option behaves the same as a multi-letter option. When used with a single dash, a single-letter option is accepted. If the option has a parameter, that must be "stuck" to the option without any intervening space or "=":

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

To set timeout to 5, use either of the following: --timeout=5, --timeout 5, --t=5, --t 5, or -t5. Forms such as -t 5 and -timeout=5 will be not accepted.

For more details about short options, refer also to the next section.

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: int;
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

dchar optionChar;
The option character (default '-').

Defaults to '-' but it can be assigned to prior to calling getopt.

string endOfOptions;
The string that conventionally marks the end of all options (default '--').

Defaults to "--" but can be assigned to prior to calling getopt. Assigning an empty string to endOfOptions effectively disables it.

dchar assignChar;
The assignment character used in options with parameters (default '=').

Defaults to '=' but can be assigned to prior to calling getopt.