docopt.cpp
: A C++11 Port.. contents:: :local: :depth: 3
Isn't it awesome how getopt
(and boost::program_options
for you fancy
folk!) generate help messages based on your code?! These timeless functions
have been around for decades and have proven we don't need anything better, right?
Hell no! You know what's awesome? It's when the option parser is generated based on the beautiful help message that you write yourself! This way you don't need to write this stupid repeatable parser-code, and instead can write only the help message--the way you want it.
docopt helps you create most beautiful command-line interfaces easily:
.. code:: c++
#include "docopt.h"
#include <iostream>
static const char USAGE[] =
R"(Naval Fate.
Usage:
naval_fate ship new <name>...
naval_fate ship <name> move <x> <y> [--speed=<kn>]
naval_fate ship shoot <x> <y>
naval_fate mine (set|remove) <x> <y> [--moored | --drifting]
naval_fate (-h | --help)
naval_fate --version
Options:
-h --help Show this screen.
--version Show version.
--speed=<kn> Speed in knots [default: 10].
--moored Moored (anchored) mine.
--drifting Drifting mine.
)";
int main(int argc, const char** argv)
{
std::map<std::string, docopt::value> args
= docopt::docopt(USAGE,
{ argv + 1, argv + argc },
true, // show help if requested
"Naval Fate 2.0"); // version string
for(auto const& arg : args) {
std::cout << arg.first << arg.second << std::endl;
}
return 0;
}
Beat that! The option parser is generated based on the docstring above
that is passed to docopt::docopt
function. docopt
parses the usage
pattern ("Usage: ..."
) and option descriptions (lines starting
with a dash "-
") and ensures that the program invocation matches the
usage pattern; it parses options, arguments and commands based on
that. The basic idea is that a good help message has all necessary
information in it to make a parser.
To get docopt.cpp, the simplest is to use Conda <https://github.com/conda-forge/docopt.cpp-feedstock>
_::
conda install -c conda-forge docopt.cpp
Alternatively manual installation is done using (unix)::
git clone
cmake .
make install
To link docopt.cpp, the simplest is to use CMake. The general structure of your
CMakeLists.txt
would be as follows::
cmake_minimum_required(VERSION 3.1)
project(example)
find_package(docopt COMPONENTS CXX REQUIRED)
include_directories(${DOCOPT_INCLUDE_DIRS})
add_executable(${PROJECT_NAME} ...)
target_link_libraries(${PROJECT_NAME} docopt)
This is a port of the docopt.py
module (https://github.com/docopt/docopt),
and we have tried to maintain full feature parity (and code structure) as the
original.
This port is written in C++11 and also requires a good C++11 standard library
(in particular, one with regex
support). The following compilers are known
to work with docopt:
GCC-4.8 can work, but the std::regex module needs to be replaced with Boost.Regex
.
In that case, you will need to define DOCTOPT_USE_BOOST_REGEX
when compiling
docopt, and link your code with the appropriated Boost libraries. A relatively
recent version of Boost is needed: 1.55 works, but 1.46 does not for example.
This port is licensed under the MIT license, just like the original module. However, we are also dual-licensing this code under the Boost License, version 1.0, as this is a popular C++ license. The licenses are similar and you are free to use this code under the terms of either license.
The differences from the Python port are:
docopt_parse
function, which does not terminatedocopt::value
type to hold the various value types that can be parsed.std::regex
does not have an equivalent to Python's regex.split,.. code:: c++
docopt::docopt(doc, argv, help /* =true */, version /* ="" */, options_first /* =false */)
docopt
takes 2 required and 3 optional arguments:
doc
is a string that contains a help message that will be parsed to.. code:: c++
R"(Usage: my_program [-hso FILE] [--quiet | --verbose] [INPUT ...]
-h --help show this
-s --sorted sorted output
-o FILE specify output file [default: ./test.txt]
--quiet print less text
--verbose print more text
)"
argv
is a vector of strings representing the args passed. Although
main usually takes a (int argc, const char** argv)
pair, you can
pass the value {argv+1, argv+argc}
to generate the vector automatically.
(Note we skip the argv[0] argument!) Alternatively you can supply a list of
strings like { "--verbose", "-o", "hai.txt" }
.
help
, by default true
, specifies whether the parser should
automatically print the help message (supplied as doc
) and
terminate, in case -h
or --help
option is encountered
(options should exist in usage pattern, more on that below). If you
want to handle -h
or --help
options manually (as other
options), set help=false
.
version
, by default empty, is an optional argument that
specifies the version of your program. If supplied, then, (assuming
--version
option is mentioned in usage pattern) when parser
encounters the --version
option, it will print the supplied
version and terminate. version
could be any printable object,
but most likely a string, e.g. "2.1.0rc1"
.
Note, when docopt
is set to automatically handle -h
,
--help
and --version
options, you still need to mention
them in usage pattern for this to work (also so your users to
know about them!)
options_first
, by default false
. If set to true
will
disallow mixing options and positional argument. I.e. after first
positional argument, all arguments will be interpreted as positional
even if the look like options. This can be used for strict
compatibility with POSIX, or if you want to dispatch your arguments
to other programs.
The return value is a map<string, docopt::value>
with options,
arguments and commands as keys, spelled exactly like in your help message.
Long versions of options are given priority. For example, if you invoke the
top example as::
naval_fate ship Guardian move 100 150 --speed=15
the return dictionary will be:
.. code:: python
{"--drifting": false, "mine": false,
"--help": false, "move": true,
"--moored": false, "new": false,
"--speed": "15", "remove": false,
"--version": false, "set": false,
"<name>": ["Guardian"], "ship": true,
"<x>": "100", "shoot": false,
"<y>": "150"}
If any parsing error (in either the usage, or due to incorrect user inputs) is encountered, the program will exit with exit code -1.
Note that there is another function that does not exit on error, and instead will propagate an exception that you can catch and process as you like. See the docopt.h file for information on the exceptions and usage:
.. code:: c++
docopt::docopt_parse(doc, argv, help /* =true */, version /* =true */, options_first /* =false)
Help message consists of 2 parts:
Usage pattern, e.g.::
Usage: my_program [-hso FILE] [--quiet | --verbose] [INPUT ...]
Option descriptions, e.g.::
-h --help show this -s --sorted sorted output -o FILE specify output file [default: ./test.txt] --quiet print less text --verbose print more text
Their format is described below; other text is ignored.
Usage pattern is a substring of doc
that starts with
usage:
(case insensitive) and ends with a visibly empty line.
Minimum example:
.. code:: python
"""Usage: my_program
"""
The first word after usage:
is interpreted as your program's name.
You can specify your program's name several times to signify several
exclusive patterns:
.. code:: python
"""Usage: my_program FILE
my_program COUNT FILE
"""
Each pattern can consist of the following elements:
my_program CONTENT-PATH
or wordsmy_program <content-path>
.-
), e.g.--output
, -o
. You can "stack" several of one-letter-oiv
which will be the same as -o -i -v
. The--input=FILE
or -i FILE
or-iFILE
. However it is important that you specify option--options
or <arguments>
or ARGUMENTS
,-
" and double dash "--
"Use the following constructs to specify patterns:
my_program [-hvqo FILE]
my_program --path=<path> <file>...
is the same as my_program (--path=<path> <file>...)
. (Note, "required options" might be notmy_program (--clockwise | --counter-clockwise) TIME
. Groupmy_program [--left | --right]
....
), e.g. my_program FILE ...
means one orFILE
-s are accepted. If you want to accept zero or moremy_program [FILE ...]
. Ellipsis[--]
". Double dash "--
" is used by convention to separate[--]
" to your usage patterns.[-]
". Single dash "-
" is used by convention to signify thatstdin
is used instead of a file. To support this add "[-]
"-
" acts as a normal command.If your pattern allows to match argument-less option (a flag) several times::
Usage: my_program [-v | -vv | -vvv]
then number of occurrences of the option will be counted. I.e.
args['-v']
will be 2
if program was invoked as my_program -vv
. Same works for commands.
If your usage pattern allows to match same-named option with argument or positional argument several times, the matched arguments will be collected into a list::
Usage: my_program <file> <file> --path=<path>...
I.e. invoked with my_program file1 file2 --path=./here --path=./there
the returned dict will contain args['<file>'] == ['file1', 'file2']
and args['--path'] == ['./here', './there']
.
Option descriptions consist of a list of options that you put below your usage patterns.
It is necessary to list option descriptions in order to specify:
The rules are as follows:
Every line in doc
that starts with -
or --
(not counting
spaces) is treated as an option description, e.g.::
Options: --verbose # GOOD -o FILE # GOOD Other: --bad # BAD, line does not start with dash "-"
To specify that option has an argument, put a word describing that
argument after space (or equals "=
" sign) as shown below. Follow
either or UPPER-CASE convention for options'
arguments. You can use comma if you want to separate options. In
the example below, both lines are valid. However you are recommended
to stick to a single style.::
-o FILE --output=FILE # without comma, with "=" sign -i , --input # with comma, without "=" sing
Use two spaces to separate options with their informal description::
--verbose More text. # BAD, will be treated as if verbose option had # an argument "More", so use 2 spaces instead -q Quit. # GOOD -o FILE Output file. # GOOD --stdout Use stdout. # GOOD, 2 spaces
If you want to set a default value for an option with an argument,
put it into the option-description, in form [default: <my-default-value>]
::
--coefficient=K The K coefficient [default: 2.95] --output=FILE Output file [default: test.txt] --directory=DIR Some directory [default: ./]
If the option is not repeatable, the value inside [default: ...]
will be interpreted as string. If it is repeatable, it will be
split into a list on whitespace::
Usage: my_program [--repeatable= --repeatable=] [--another-repeatable=]... [--not-repeatable=]
--repeatable= [default: ./here ./there]
--another-repeatable= [default: ./here]
--not-repeatable= [default: ./here ./there]
We have an extensive list of examples <https://github.com/docopt/docopt/tree/master/examples>
_ which cover
every aspect of functionality of docopt. Try them out, read the
source if in doubt.
There are also very interesting applications and ideas at that page. Check out the sister project for more information!
If you want to split your usage-pattern into several, implement
multi-level help (with separate help-screen for each subcommand),
want to interface with existing scripts that don't use docopt, or
you're building the next "git", you will need the new options_first
parameter (described in API section above). To get you started quickly
we implemented a subset of git command-line interface as an example:
examples/git <https://github.com/docopt/docopt/tree/master/examples/git>
_
The original Python module includes some language-agnostic unit tests, and these can be run with this port as well.
The tests are a Python driver that uses the testcases.docopt file to then invoke a C++ test case runner (run_testcase.cpp)::
$ clang++ --std=c++11 --stdlib=libc++ docopt.cpp run_testcase.cpp -o run_testcase $ python run_tests.py PASS (175)
You can also compile the example shown at the start (included as example.cpp)::
$ clang++ --std=c++11 --stdlib=libc++ -I . docopt.cpp examples/naval_fate.cpp -o naval_fate $ ./naval_fate --help [ ... ] $ ./naval_fate ship Guardian move 100 150 --speed=15 --drifting: false --help: false --moored: false --speed: "15" --version: false : ["Guardian"] : "100" : "150" mine: false move: true new: false remove: false set: false ship: true shoot: false
Comments and suggestions are very welcome! If you find issues, please file them and help improve our code!
Please note, however, that we have tried to stay true to the original Python code. If you have any major patches, structural changes, or new features, we might want to first negotiate these changes into the Python code first. However, bring it up! Let's hear it!
docopt follows semantic versioning <http://semver.org>
_. The
first release with stable API will be 1.0.0 (soon).