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CLI11 provides all the features you expect in a powerful command line parser, with a beautiful, minimal syntax and no dependencies beyond C++11. It is header only, and comes in a single file form for easy inclusion in projects. It is easy to use for small projects, but powerful enough for complex command line projects, and can be customized for frameworks.It is tested onTravis andAppVeyor, and is being included in theGooFit GPU fitting framework. It was inspired byplumbum.cli for Python. CLI11 has a user friendly introduction in this README, a more in-depth tutorialGitBook, as well asAPI documentation generated by Travis.See thechangelog orGitHub Releases for details for current and past releases. Also see theVersion 1.0 post andVersion 1.3 post for more information.

You can be notified when new releases are made by subscribing tohttps://github.com/CLIUtils/CLI11/releases.atom on an RSS reader, like Feedly.

An acceptable CLI parser library should be all of the following:

• Easy to include (i.e., header only, one file if possible,no external requirements): While many programs depend on Boost, that should not be a requirement if all you want is CLI parsing.
• Short Syntax: This is one of the main points of a CLI parser, it should make variables from the command line nearly as easy to define as any other variables. If most of your program is hidden in CLI parsing, this is a problem for readability.
• C++11 or better: Should work with GCC 4.7+ (such as GCC 4.8 on CentOS 7) or above, or Clang 3.5+, or MSVC 2015+. (Note: for CLI11, Clang 3.4 only fails because of tests, GoogleMock does not support it.)
• Work on Linux, macOS, and Windows.
• Well tested usingTravis (Linux and macOS) andAppVeyor (Windows). "Well" is defined as having good coverage measured byCodeCov.
• Clear help printing.
• Nice error messages.
• Standard shell idioms supported naturally, like grouping flags, a positional separator, etc.
• Easy to execute, with help, parse errors, etc. providing correct exit and details.
• Easy to extend as part of a framework that provides "applications" to users.
• Usable subcommand syntax, with support for multiple subcommands, nested subcommands, and optional fallthrough (explained later).
• Ability to add a configuration file (ini format), and produce it as well.
• Produce real values that can be used directly in code, not something you have pay compute time to look up, for HPC applications.
• Work with standard types, simple custom types, and extendible to exotic types.
• Permissively licensed.

None of these libraries fulfill all the above requirements, or really even come close. As you probably have already guessed, CLI11 does.So, this library was designed to provide a great syntax, good compiler compatibility, and minimal installation fuss.

There are some other possible "features" that are intentionally not supported by this library:

• Non-standard variations on syntax, like-long options. This is non-standard and should be avoided, so that is enforced by this library.
• Completion of partial options, such as Python'sargparse supplies for incomplete arguments. It's better not to guess. Most third party command line parsers for python actually reimplement command line parsing rather than using argparse because of this perceived design flaw.
• In C++14, you could have a set ofcallback methods with differing signatures (tested in a branch). Not deemed worth having a C++14 variation on API and removed.
• Autocomplete: This might eventually be added to both Plumbum and CLI11, but it is not supported yet.
• Wide strings / unicode: Since this uses the standard library only, it might be hard to properly implement, but I would be open to suggestions in how to do this.

To use, there are two methods:

1. CopyCLI11.hpp from themost recent release into your include directory, and you are set. This is combined from the source files for every release. This includes the entire command parser library, but does not include separate utilities (likeTimer,AutoTimer). The utilities are completely self contained and can be copied separately.
2. Checkout the repository and add as a subdirectory for CMake. You can use theCLI11 interface target when linking. (CMake 3.4+ required, 3.10+ best) Or, instead of explicitly downloading the library, use theAddCLI.cmake supplied inCLIUtils cmake helpers.

To build the tests, checkout the repository and use CMake:

mkdir buildcd buildcmake ..makeGTEST_COLOR=1 CTEST_OUTPUT_ON_FAILURE=1 maketest

To set up, add options, and run, your main function will look something like this:

CLI::App app{"App description"};std::string filename ="default";app.add_option("-f,--file", filename,"A help string");CLI11_PARSE(app, argc, argv);

try {    app.parse(argc, argv);}catch (const CLI::ParseError &e) {return app.exit(e);}

The initialization is just one line, adding options is just two each. The parse macro is just one line (or 5 for the contents of the macro). After the app runs, the filename will be set to the correct value if it was passed, otherwise it will be set to the default. You can check to see if this was passed on the command line withapp.count("--file").

The supported values are:

app.add_options(option_name,                variable_to_bind_to,// int, float, vector, or string-like                help_string="",default=false)app.add_complex(...// Special case: support for complex numbersapp.add_flag(option_name,             int_or_bool = nothing,             help_string="")app.add_flag_function(option_name,             function <void(size_t count)>,             help_string="")app.add_set(option_name,            variable_to_bind_to,            set_of_possible_options,            help_string="",default=false)app.add_set_ignore_case(...// String onlyApp* subcom = app.add_subcommand(name, discription);

An option name must start with a alphabetic character or underscore. For long options, anything but an equals sign or a comma is valid after that. Names are given as a comma separated string, with the dash or dashes. An option or flag can have as many names as you want, and afterward, usingcount, you can use any of the names, with dashes as needed, to count the options. One of the names is allowed to be given without proceeding dash(es); if present the option is a positional option, and that name will be used on help line for its positional form. If you want the default value to print in the help description, pass intrue for the final parameter foradd_option oradd_set. The set options allow your users to pick from a set of predefined options.

On a C++14 compiler, you can pass a callback function directly to.add_flag, while in C++11 mode you'll need to use.add_flag_function if you want a callback function. The function will be given the number of times the flag was passed. You can throw a relevantCLI::ParseError to signal a failure.

• "one,-o,--one": Valid as long as not a flag, would create an option that can be specified positionally, or with-o or--one
• "this" Can only be passed positionally
• "-a,-b,-c" No limit to the number of non-positional option names

The add commands return a pointer to an internally storedOption. If you set the final argument to true, the default value is captured and printed on the command line with the help flag. This option can be used directly to check for the count (->count()) after parsing to avoid a string based lookup. Before parsing, you can set the following options:

• ->required(): The program will quit if this option is not present. This ismandatory in Plumbum, but required options seems to be a more standard term. For compatibility,->mandatory() also works.
• ->expected(N): TakeN values instead of as many as possible, only for vector args. If negative, require at least-N.
• ->requires(opt): This option requires another option to also be present, opt is anOption pointer.
• ->excludes(opt): This option cannot be given withopt present, opt is anOption pointer.
• ->envname(name): Gets the value from the environment if present and not passed on the command line.
• ->group(name): The help group to put the option in. No effect for positional options. Defaults to"Options"."" will not show up in the help print (hidden).
• ->ignore_case(): Ignore the case on the command line (also works on subcommands, does not affect arguments).
• ->multi_option_policy(CLI::MultiOptionPolicy::Throw): Set the multi-option policy. Shortcuts available:->take_last(),->take_first(), and->join(). This will only affect options expecting 1 argument or bool flags (which always default to take last).
• ->check(CLI::ExistingFile): Requires that the file exists if given.
• ->check(CLI::ExistingDirectory): Requires that the directory exists.
• ->check(CLI::NonexistentPath): Requires that the path does not exist.
• ->check(CLI::Range(min,max)): Requires that the option be between min and max (make sure to use floating point if needed). Min defaults to 0.
• ->transform(std::string(std::string)): Converts the input string into the output string, in-place in the parsed options.
• ->configurable(false): Disable this option from being in an ini configuration file.

These options return theOption pointer, so you can chain them together, and even skip storing the pointer entirely. Check takes any function that has the signaturevoid(const std::string&); it should throw aValidationError when validation fails. The help message will have the name of the parent option prepended. Sincecheck andtransform use the same underlying mechanism, you can chain as many as you want, and they will be executed in order. If you just want to see the unconverted values, use.results() to get thestd::vector<std::string> of results.

On the command line, options can be given as:

• -a (flag)
• -abc (flags can be combined)
• -f filename (option)
• -ffilename (no space required)
• -abcf filename (flags and option can be combined)
• --long (long flag)
• --file filename (space)
• --file=filename (equals)

Extra positional arguments will cause the program to exit, so at least one positional option with a vector is recommended if you want to allow extraneous arguments.If you set.allow_extras() on the mainApp, you will not get an error. You can access the missing options usingremaining (if you have subcommands,app.remaining(true) will get all remaining options, subcommands included).

You can access a vector of pointers to the parsed options in the original order usingparse_order().If-- is present in the command line,everything after that is positional only.

Subcommands are supported, and can be nested infinitely. To add a subcommand, call theadd_subcommand method with a name and an optional description. This gives a pointer to anApp that behaves just like the main app, and can take options or further subcommands. Add->ignore_case() to a subcommand to allow any variation of caps to also be accepted. Children inherit the current setting from the parent. You cannot add multiple matching subcommand names at the same level (including ignorecase).

If you want to require that at least one subcommand is given, use.require_subcommand() on the parent app. You can optionally give an exact number of subcommands to require, as well. If you give two arguments, that sets the min and max number allowed.0 for the max number allowed will allow an unlimited number of subcommands. As a handy shortcut, a single negative value N will set "up to N" values. Limiting the maximimum number allows you to keep arguments that match a previoussubcommand name from matching.

If anApp (main or subcommand) has been parsed on the command line,->parsed will be true (or convert directly to bool).AllApps have aget_subcommands() method, which returns a list of pointers to the subcommands passed on the command line. Agot_subcommand(App_or_name) method is also provided that will check to see if anApp pointer or a string name was collected on the command line.

For many cases, however, using an app's callback may be easier. Every app executes a callback function after it parses; just use a lambda function (with capture to get parsed values) to.set_callback. If you throwCLI::Success orCLI::RuntimeError(return_value), you caneven exit the program through the callback. The mainApp has a callback slot, as well, but it is generally not as useful.You are allowed to throwCLI::Success in the callbacks.Multiple subcommands are allowed, to allowClick like series of commands (order is preserved).

There are several options that are supported on the main app and subcommands. These are:

• .ignore_case(): Ignore the case of this subcommand. Inherited by added subcommands, so is usually used on the mainApp.
• .fallthrough(): Allow extra unmatched options and positionals to "fall through" and be matched on a parent command. Subcommands always are allowed to fall through.
• .require_subcommand(): Require 1 or more subcommands.
• .require_subcommand(N): RequireN subcommands ifN>0, or up toN ifN<0.N=0 resets to the default 0 or more.
• .require_subcommand(min, max): Explicitly set min and max allowed subcommands. Settingmax to 0 is unlimited.
• .add_subcommand(name, description="") Add a subcommand, returns a pointer to the internally stored subcommand.
• .got_subcommand(App_or_name): Check to see if a subcommand was received on the command line
• .get_subcommands(): The list of subcommands given on the command line
• .get_parent(): Get the parent App or nullptr if called on master AppComing in version 1.4
• .parsed(): True if this subcommand was given on the command line
• .set_callback(void() function): Set the callback that runs at the end of parsing. The options have already run at this point.
• .allow_extras(): Do not throw an error if extra arguments are left over
• .prefix_command(): Likeallow_extras, but stop immediately on the first unrecognised item. It is ideal for allowing your app or subcommand to be a "prefix" to calling another app.
• .set_footer(message): Set text to appear at the bottom of the help string.
• .set_failure_message(func): Set the failure message function. Two provided:CLI::FailureMessage::help andCLI::FailureMessage::simple (the default).
• .group(name): Set a group name, defaults to"Subcommands". Setting"" will be hide the subcommand.

Note: if you have a fixed number of required positional options, that will match before subcommand names.

app.set_config(option_name="",               default_file_name="",               help_string="Read an ini file",               required=false)

If this is called with no arguments, it will remove the configuration file option (likeset_help_flag). Setting a configuration option is special. If it is present, it will be read along with the normal command line arguments. The file will be read if it exists, and does not throw an error unlessrequired istrue. Configuration files are inini format. An example of a file:

; Commments are supported, using a ;; The default section is [default], case insensitivevalue = 1str ="A string"vector = 1 2 3; Section map to subcommands[subcommand]in_subcommand = Wowsub.subcommand = true

Spaces before and after the name and argument are ignored. Multiple arguments are separated by spaces. One set of quotes will be removed, preserving spaces (the same way the command line works). Boolean options can betrue,on,1,yes; orfalse,off,0,no (case insensitive). Sections (and. separated names) are treated as subcommands (note: this does not mean that subcommand was passed, it just sets the "defaults". To print a configuration file from the passedarguments, use.config_to_str(default_also=false), wheredefault_also will also show any defaulted arguments.

Many of the defaults for subcommands and even options are inherited from their creators. The inherited default values for subcommands areallow_extras,prefix_command,ignore_case,fallthrough,group,footer, and maximum number of required subcommands. The help flag existence, name, and description are inherited, as well.

Options have defaults forgroup,required,multi_option_policy, andignore_case. To set these defaults, you should set theoption_defaults() object, for example:

app.option_defaults()->required();// All future options will be required

The default settings for options are inherited to subcommands, as well.

The App class was designed allow toolkits to subclass it, to provide preset default options (see above) and setup/teardown code. Subcommands remain an unsubclassedApp, since those are not expected to need setup and teardown. The defaultApp only adds a help flag,-h,--help, than can removed/replaced using.set_help_flag(name, help_string). You can remove options if you have pointers to them using.remove_option(opt). You can add apre_callback override to customize the after parsebut before run behavior, whilestill giving the user freedom toset_callback on the main app.

The most important parse function isparse(std::vector<std::string>), which takes a reversed list of arguments (so thatpop_back processes the args in the correct order).get_help_ptr andget_config_ptr give you access to the help/config option pointers. The standardparse manually sets the name from the first argument, so it should not be in this vector.

Also, in a related note, theApp you get a pointer to is stored in the parentApp in aunique_ptrs (likeOptions) and are deleted when the mainApp goes out of scope.

Everyadd_ option you have seen so far depends on one method that takes a lambda function. Each of these methods is just making a different lambda function with capture to populate the option. The function has full access to the vector of strings, so it knows how many times an option was passed or how many arguments it received (flags add empty strings to keep the counts correct). The lambda returnstrue if it could validate the option strings, andfalse if it failed. If you wanted to extend this to support a new type, just use a lambda. An example of a new parser forcomplex<double> that supports all of the features of a standardadd_options call is inone of the tests. A simpler example is shown below:

app.add_option("--fancy-count", [](std::vector<std::string> val){    std::cout <<"This option was given" << val.size() <<" times." << std::endl    });

There are a few other utilities that are often useful in CLI programming. These are in separate headers, and do not appear inCLI11.hpp, but are completely independent and can be used as needed. TheTimer/AutoTimer class allows you to easily time a block of code, with custom print output.

{CLI::AutoTimer timer {"My Long Process", CLI::Timer::Big};some_long_running_process();}

This will create a timer with a title (default:Timer), and will customize the output using the predefinedBig output (default:Simple). Because it is anAutoTimer, it will print out the time elapsed when the timer is destroyed at the end of the block. If you useTimer instead, you can useto_string orstd::cout << timer << std::endl; to print the time. The print function can be any function that takes two strings, the title and the time, and returns a formattedstring for printing.

If you use the excellentRang library to add color to your terminal in a safe, multi-platform way, you can combine it with CLI11 nicely:

std::atexit([](){std::cout << rang::style::reset;});try {    app.parse(argc, argv);}catch (const CLI::ParseError &e) {    std::cout << (e.get_exit_code()==0 ? rang::fg::blue : rang::fg::red);return app.exit(e);}

This will print help in blue, errors in red, and will reset before returning the terminal to the user.

If you are on a Unix-like system, and you'd like to handle control-c and color, you can add:

 #include<csignal>voidsignal_handler(int s) {     std::cout << std::endl << rang::style::reset << rang::fg::red << rang::fg::bold;     std::cout <<"Control-C detected, exiting..." << rang::style::reset << std::endl;std::exit(1);// will call the correct exit func, no unwinding of the stack though }

And, in your main function:

// Nice Control-Cstructsigaction sigIntHandler;     sigIntHandler.sa_handler = signal_handler;sigemptyset(&sigIntHandler.sa_mask);     sigIntHandler.sa_flags =0;sigaction(SIGINT, &sigIntHandler,nullptr);

To contribute, open anissue orpull request on GitHub, or ask a question ongitter. The is also a short note to contributorshere.

As of version 1.0, this library is available under a 3-Clause BSD license. See theLICENSE file for details.

This project was created by Henry Schreiner. Significant features and/or improvements to the code were contributed by:

• Marcus Brinkmann

CLI11 was developed at theUniversity of Cincinnati to support of theGooFit library underNSF Award 1414736. Version 0.9 was featured in aDIANA/HEP meeting at CERN (see the slides). Please give it a try! Feedback is always welcome.